Single-Parent Upbringing as a Predictor of Long-
Term Violence Scale in Solo Male Serial Killers
Chapter 1: Introduction
The perpetration of violence by humans against humans has occurred
as long as humans have existed. The quest to identify factors that reliably
contribute to violent behavior—particularly extreme, recurrent violence—
persists. Researchers have repeatedly identified the critical role of parenting
quality in children’s short- and longterm maladaptive behavioral outcomes
(Mathews & Abrahams, 2018; Sulima, 2019). As a result of temporal and
financial resource limitations and increased demands on single parents,
children who grow up in single-parent households may be particularly
vulnerable to conditions that foster long-term violent behavior. Although
researchers associate growing up in a single-parent household with violent
behavior, the magnitude and pervasiveness of the violence associated with a
single-parent upbringing is relatively unexplored (Heleniak & McLaughlin,
2019). Examination of the relative scale of violence perpetrated by male
serial killers raised by single parents may facilitate more precise insight into
the characteristics of the parent-child relationship that tend to contribute to
large-scale violent behavior over time. By further dissecting the relationship
between single-parent households and the perpetration of extreme, recurrent
violence over the course of a lifetime, researchers may identify yet-
unexplored parental behaviors or household conditions that play a significant
role in the psychology of a developing serial killer.
The background section of this chapter briefly covers previous
research of the association between single-parent households and negative
psychological and behavioral outcomes, and the knowledge gap is set forth.
In the problem statement section, I state the research problem and
summarize evidence of its relevance and significance. The following section
provides the purpose statement and the independent and dependent variables
the quantitative study includes. The research questions and hypotheses are
stated, followed by a discussion of the theoretical framework for the study.
In the nature of the study section, I outline the rationale for the study, briefly
describe the variables of study, and summarize the methodology to be used.
Definitions of the independent and dependent variables are provided before I
state the assumptions I made in conducting the study and why I made those
assumptions. The scope and delimitation section includes the scope of the
study and the rationale for choices I made in designing the study. In the
limitations section, I describe methodological weaknesses and measures I
took to address them. In the significance section, I suggest potential
contributions of the study to understanding the association between a single-
parent household in childhood and longterm extreme and recurrent violence.
Finally, the main points of the chapter are briefly summarized.
Background
Nearly one fourth of children in the United States live in single-parent
households (Pew Research Center, 2019). Growing up in a single-parent
household is associated with exposure to adverse childhood experiences
(ACEs; Jackson, Choi, & Preston, 2019; Manjunatha, Chandrashekar, &
Chandrashekhara, 2019; Rousou, Kouta, Middleton, & Karanikola, 2019).
For example, children in single-parent homes may experience adverse
psychological impacts from an absent parent (Mok et al., 2018), exposure to
unsafe or age-inappropriate situations due to poor supervision (Ben-David,
2016), and overtly harsh or withdrawn parenting behaviors by a burdened
and poorly coping single parent (Jackson et al., 2019; Mathews &
Abrahams, 2018).
Previous researchers have correlated a single-parent upbringing and
myriad negative short- and long-term psychological and behavioral
outcomes. These range from psychological distress (Clements-Noelle &
Waddington, 2019; Sinha & Ram, 2019) and interpersonal problems
(Hinojosa, Hinojosa, Bright, & Nguyen, 2019; Nawaz, Ali, Najmussaqib,
Ahmed, & Rehna, 2019), to juvenile delinquency (Burlaka, 2016; Dijanic,
2016) and, ultimately, violence (Heleniak & McLaughlin, 2019). Although
an association between growing up in a single-parent home and violent
behavior has been established, the scale of violence perpetrated by offenders
raised by a single parent remains unknown. I conducted this quantitative
study to investigate the scale or magnitude of the violence associated with
offenders raised by a single parent. More clearly understanding the relative
violence level that children raised in single-parent households may be at
increased risk of perpetrating may contribute to a better-informed narrative
regarding the risks of single-parent households. Further, more focused and
effective intervention strategies may be developed and implemented with
children at elevated long-term violence risk.
Problem Statement
Researchers have established a clear association between growing up
in a singleparent household and myriad maladaptive psychological and
behavioral outcomes that may endure throughout adulthood (Fergusson,
Boden, & Horwood, 2007). Although the single-parent/violence link has
been empirically established, there has been little or no research on the scale
of violence perpetrated by violent offenders from single-parent backgrounds.
The dissection of the violence linked to single-parent households through an
examination of violence extensiveness (i.e., number of victims suspected,
number of victims confessed to, number of victims convicted of, duration)
among serially violent offenders will help elucidate the predictive
relationship between a single-parent upbringing and recurrent and extreme
violent behavior throughout adulthood. With nearly one quarter of children
in the United States growing up in a single-parent home, it is imperative to
fully understand the long-term, potentially violent implications of the single-
parent household.
Purpose Statement
The purpose of this study was to examine the scale of the violence
correlated with a single-parent upbringing. Expanding on prior research
establishing the correlation between growing up in a single-parent household
and violent behavior, I dissected the scale of the associated violence. Solo,
male serial homicide offenders who, through previous research, have been
identified as having grown up in a single-parent home were the subjects of
this study. Scale of violence was measured through four variables: (a)
number of suspected victims, (b) number of victims confessed to, (c) number
of victims convicted of, (d) duration. I explored the psychological path from
single-parent-related ACE exposure to the ultimate violent behavioral
outcomes using interpersonal acceptance and rejection theory (IPARTheory;
Rohner, 1986) as a theoretical lens. The results of this study can provide a
more nuanced understanding of the relationship between a singleparent
household upbringing and the scale (e.g., number of suspected victims,
number of victims confessed to, number of victims convicted of, duration) of
correlated violence among male solo serial killers in adulthood.
Research Questions and Hypotheses
RQ1: Does growing up in a single-parent household predict the
number of victims solo male serial killers are suspected to have killed?
H 01: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are suspected of killing.
H a1: Growing up in a single-parent household does predict the number
of victims solo male serial killers are suspected of killing.
RQ2: Does growing up in a single-parent household predict the
number of victims solo male serial killers confess to killing?
H 02: Growing up in a single-parent household does not predict the
number of victims solo male serial killers confess to killing.
H a2: Growing up in a single-parent household does predict the
number of victims solo male serial killers confess to killing.
RQ3: Does growing up in a single-parent household predict the
number of victims solo male serial killers are convicted of killing?
H 03: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are convicted of killing.
H a3: Growing up in a single-parent household does predict the
number of victims solo male serial killers are convicted of killing.
RQ4: Does growing up in a single-parent household predict the
duration of homicide perpetration among solo male serial killers?
H 04: Growing up in a single-parent household does not predict the
duration of homicide perpetration among solo male serial killers.
H a4: Growing up in a single-parent household does predict the
duration of homicide perpetration among solo male serial killers.
Theoretical Framework
The theoretical basis for this study was Rohner’s (1986, 2016)
IPARTheory, which indicates that irrespective of parental intent, parental
behaviors and household conditions interpreted by a child as abusive,
neglectful, or indifferent contribute to perceptions of rejection (Rohner &
Lansford, 2017). Significant research supports the notion that a child’s
perception of parental rejection as a function of an ACE, rather than an ACE
itself, contributes to short- and long-term negative behavioral outcomes
(Khaleque, 2017; Smeijers, Brazil, Bulten, & Verkes, 2018). Thus,
IPARTheory offers a psychological framework for understanding the path
from ACE, such as those that may accompany a single-parent household, to
long-term negative behavioral outcomes, such as homicidal violence.
Nature of Study
In this study, I employed a nonexperimental, cross-sectional design to
assess the correlations between growing up in a single-parent household and
scale of violence for statistical significance. Nonexperimental research is
appropriate when the independent variable is not manipulated. Instead, the
relationships between variables are measured as they naturally exist
(Thompson, 2007). Because the circumstances of an individual’s upbringing
cannot be experimentally manipulated, a nonexperimental design was
appropriate.
To examine the role of single-parent household on violence scale
without manipulating the independent variable, I used a cross-sectional
design. Cross-sectional designs enable the comparison of two preexisting
groups of people based on the presence or absence of the independent
variable (Mann, 2003). By comparing male serial killers who were raised in
a single-parent home with those who were not, the role that a singleparent
upbringing has on the dependent variable, violence scale, may be more
precisely described.
Archival secondary data contained in the Radford/FGCU Serial Killer
Database were analyzed (Radford University/Florida Gulf Coast University,
2015). The database is the accumulation of multiple serial killer researchers’
independent findings. The database serves as a response to Kiger’s (1990)
call to develop robust sources for empirical serial killer research, satisfying
in part the historical difficulty with researching serial homicide (Yaksic,
2016). The independent and dependent variables in this study are included in
the database.
Definitions
Confessed homicide: An admission to the perpetration of a homicide
(18 U.S.C. § 3501[e]).
Convicted homicide: Homicide for which a formal judgment of guilt is
entered by a court (Federal Rules of Criminal Procedure, Title VI, Rule 31).
Scale of violence: The magnitude or extent of some phenomenon, such
as through the measure of quantity (Blanchet, Ceresetti, Molinié, & Creutin,
2016; Salamon, Davies, Fuentes, Weisman, & Hainsworth, 2014).
Single-parent household: A child’s primary residence in which only
one of a child’s biological parents resides (Pew Research Center, 2015).
Suspected homicide: Homicide which law enforcement officials
believe, based on evidence, an offender committed but for which the
offender did not confess and was not legally convicted (18 U.S.C. § 3103a).
Violence duration: Number of years in the span of time in which the
offender perpetrated homicide (Dekel, Shaked, Ben-Porat, & Itzhaky, 2019;
Godrati, Yazdanpanahi, & Akbarzadeh, 2019).
Assumptions
This study included several assumptions. First, I assumed the
methodological rigor of this data. For instance, I assumed the primary data
collection methods were sound, the relevant constructs (raised by birth
mother only, raised by birth father only, number of homicides perpetrated,
years of first and last known homicide, and number of known victims) were
measured in a way that the data are valid and reliable, and the recording of
the primary data is accurate.
Second, I assumed that external factors affecting the dependent
variables did not present a substantial danger to the validity of the research.
Specifically, the number of victims suspected, the number of victims
confessed to, the number of victims convicted of, and the duration of
homicidal behavior are influenced by how quickly the offender is
apprehended. One offender may be apprehended more quickly than another
because his crimes were committed in a well-resourced or particularly adept
law enforcement agency’s jurisdiction or because the offender took less
effective precautions to prevent being caught. As a consequence, the
offender may have committed fewer homicides over a shorter period of time,
killing fewer people than he would have if he had remained free, perhaps
artificially deflating his statistics. Although this is a threat to the study’s
validity, because this issue is inherently present among all the serial killers in
the database and is not limited to one group or another, the associated risks
are relatively evenly distributed across the data.
Scope and Delimitations
The scope of the study is the examination of two variables: single-
parent household in childhood and scale of violence. A delimitation of the
study is the choice to examine male serial killers to better understand the
relationship between a single-parent upbringing and long-term, large-scale
violent behavior. Serial homicide is only one form of long-term violence;
however, it is an extreme form and may provide the outer limits of any
identified relationships.
A second delimitation is the choice to compare male serial killers
raised in a single-parent home with serial killers raised with both birth
parents. Other categories of upbringing circumstances included in the
database are, for example, being raised by a birth parent and a stepparent, a
stepparent only, relatives, foster parents, or in an orphanage (Radford
University/Florida Gulf Coast University, 2019). To compare the effects of a
single-parent upbringing with the empirically proven ideal household
situation, which is to be raised by both parents (Behere, Basnet, & Campbell,
2017; Fallesen & Gahler, 2019; Upreti & Sharma, 2018), I chose to include
only these two groups.
A third delimitation of the study is the choice to operationalize scale
of violence as number of victims suspected, number of victims confessed to,
number of victims convicted of, and duration. Quantity, as measured by
number of victims and duration, is readily found in the literature to measure
the scale, magnitude, or extent of some phenomenon (Blanchet, Ceresetti,
Molinié, & Creutin, 2016; Salamon, Davies, Fuentes, Weisman, &
Hainsworth, 2014). Therefore, they were used as a measure of scale for this
study.
A fourth delimitation is the choice to study only solo male serial
killers in the United States. Although the database contains serial killers,
including women, partners, and groups from all over the world, I chose to
focus my population to male and solo serial killers, the most common type
of serial killers (Hickey, 2016), and to those whose crimes were committed,
at least in part, in the United States. These choices were made to improve the
generalizability of the results across serial killers within the same
demographic group. It may, however, limit generalizability to serial killers
who do not share these demographics.
Limitations
This study has limitations. First, errors or inconsistencies with the
secondary data used in the analysis may constrain the validity of the results.
The data were compiled over 20 years from multiple researchers who used
varying methodologies into a single database (Aamodt, 2015). In addition to
the potential for human error in acquiring and/or recording the relevant data,
not all the relevant variables are reported for all the serial killers in the
database. For example, there may be serial killers included in the database
who were raised by a single parent but who were not assessed on the
variable of singleparent upbringing by the primary researcher. This
limitation affects sample size.
A second limitation is the likelihood that many of the serial killers in
the database would have continued to kill if they had not been caught, in
which case the number of victims suspected, number of victims confessed to,
number of victims convicted of, and duration would have increased. The
practical effect of this limitation is that the dependent variable data are
almost certainly a conservative estimate of the data. As previously discussed,
this effect spans across most serial killers and, thus, does not likely favor one
group over another.
Significance
This study extends previous research of single-parent upbringing and
its potentially grievous impacts in three ways. First, in this study, I dissected
the construct of violence as a behavioral outcome. Existing literature
regarding the increased risk of short- and long-term negative psychological
and behavioral outcomes of single-parent households to children does not
include investigations of violence scale. Thus, although a link between a
single-parent upbringing and long-term violence has been established, it
remains unclear whether violence tends to be recurrent, endures over time,
and/or tends to claim multiple victims. A more nuanced understanding of the
extent of the singleparent/violence relationship and the psychological
underpinnings of the relationship enables a more precise narrative of the
predictive nature of the single-parent household to large-scale violence in
adulthood. As a consequence, well-informed, pointed risk assessment and
intervention strategies may be developed and implemented early in a
child’s life.
Second, I focused on adult male solo serial killers in the examination
of violent outcomes of single-parent households. Serial killing is an
inherently violent pursuit; therefore, the variable of violence outcome
necessarily exists in this population. By studying only those serial killers
who were raised in single-parent homes and analyzing various measures of
scale of their homicide perpetration, correlational relationships, to the extent
they exist, revealed themselves more clearly.
Third, I used IPARTheory (Rohner, 1986) as this study’s theoretical
framework. IPARTheory holds that it is the child’s psychological
interpretation of ACEs as parental rejection that bridges the adverse event or
enduring adverse condition to the behavioral outcome (Rohner, 1986, 2016).
By examining the single-parent/scale-of-violence relationship through the
lens of IPARTheory, a deeper layer of understanding the psychological
operation of the relationship between these variables emerged.
Summary
The goal of this study was to investigate the relationship between
growing up in a single-parent household and the scale of long-term violence
perpetration. The relative magnitude of violence perpetrated by male serial
killers, an extremely violent population, helps clarify the importance of a
potentially adverse early experience. Further, by examining this
phenomenon through the lens of IPARTheory (Rohner, 1986; 2016), a
framework for contextualizing the psychological processes driving the
negative behavior is provided. Through this study, a more nuanced
understanding of the relationship of a single-parent upbringing and large-
scale, long-term violence may be achieved.
Chapter 2: Literature Review
Introduction
Nearly 25% of children in the United States live in single-parent
households (Pew Research Center, 2019). Growing up in a single-parent
home is often treated as an adverse childhood experience (ACE) by
psychologists and courts because of the strong correlation between single-
parent households and child maltreatment (Kratsky & Schroder-Abe, 2018;
Paluch, Heard-Garris, & Carnethon, 2019). A single-parent household may
expose a child to ACEs in multiple ways: through psychological impacts of
an absentee parent; increased risk of abuse, neglect, and indifference by the
single parent; and household conditions that tend to accompany single
parenthood, such as poverty and parental depression (Afifi et al., 2015;
Mathews & Abrahams, 2018).
According to IPARTheory (Rohner, 1986), parental behaviors and
household conditions interpreted by a child as abusive, neglectful, or
indifferent—even if not the parent’s intent—contribute to perceptions of
rejection (Rohner & Lansford, 2017). A child’s perception of parental
rejection, rather than parental intent, is the critical psychological component
for maladaptive outcomes (Rohner, 1986, 2016). Such a perception is
amplified when a child depends on a single parent (Carrasco,
GonzlezCalderon, & Suarez, 2018). When a child perceives rejection by a
parent, the child’s fundamental need for emotional attachment to,
recognition by, and support from the primary caregiver goes unmet
(Humphreys, 2019; Rohner, 1986, 2016), contributing to a host of
detrimental psychological (Alenazi, Hammad, & Mohamed, 2019), cognitive
(Khaleque, Uddin, Hossain, Siddique, & Shirin, 2019), affective (Ali et al.,
2019), and behavioral (Smeijers et al., 2019) manifestations.
According to the literature, violence that begins in childhood and
persists through adulthood is an extreme-case outcome shared by offenders
from single-parent households (Fergusson, Boden, & Horwood, 2007) and
by offenders who perceive parental rejection (Woeckener et al., 2018).
Although evidence shows a direct, significant relationship between growing
up in a single-parent home and perpetrating violence, there has been little or
no research investigating the scale or extent of violence. Analysis of the
number of victims suspected, the number of victims confessed to, the
number of victims convicted of having killed, and the duration of violent
homicidal behavior among offenders raised by a single parent may clarify
the role of single-parent households in recurrent, extreme long-term
violence. Examining the strength of the relationship between growing up in a
single-parent household and the commission of extreme violence will help to
illuminate the psychological impact of single-parent homes.
Chapter 2 includes an overview of the literature search strategy I used
and a brief statement of the conceptual framework of the study. A discussion
of adverse experiences and trauma follows. The single-parent household as
an adverse childhood experience, its maladaptive outcomes, and its
contributors are discussed. Next, I delve into IPARTheory and its application
to violence, including serial killing. Finally, I summarize the major points of
Chapter 2.
Literature Search Strategy
The literature review search strategy involved the exploration of
multiple scholarly databases, Internet search engines, and websites. The
most recurrently used databases were Academic Search Complete, EBSCO,
PsycARTICLES, PsycINFO, Research Gate, SAGE Journals, ScienceDirect,
and SocINDEX. The most frequently used search engine was Google
Scholar. I used Walden University’s online library to search for relevant
article and to locate exact articles. Keyword searches included various forms
of the root words of terms including adverse childhood experiences,
IPARTheory, parental acceptance, parental rejection, perceptions of
rejection, warmth and affection, hostility and aggression, undifferentiated
rejection, parental indifference, parental disengagement, parental neglect,
child neglect, child abuse, parental absence, single parent, poverty, financial
hardship, financial instability, socioeconomic disadvantage, emotional
outcomes, social outcomes, cognitive outcomes, behavioral outcomes, anger,
criminal behavior, violence, violence intensity, scale of violence, brutality,
violence severity, homicide, murder, and serial killer (see Appendix A for a
complete list of search terms). This intensive search consisted primarily of
examining data from studies published in or after 2015. Research published
prior to 2015 was included when few subsequent studies were published on a
topic or when the research was foundational to a topic.
Theoretical Framework
Interpersonal Acceptance-Rejection Theory
IPARTheory is a theory of socialization and lifespan development
(Rohner, 1986, 2016). IPARTheory’s personality subtheory focuses on the
culturally invariant nature and effects of parental acceptance and rejection to
children over the course of their lifespan, attempting to predict and explain
the psychological consequences and personality manifestations of children’s
perceptions of parental rejection (Rohner, 1986, 2016). In this way,
IPARTheory resembles attachment theory (Ainsworth, 1973; Bowlby, 1969,
1973) in its emphasis on the quality of the connection to an attachment
figure (e.g., parent) as the basis for an individual’s feelings of emotional
security and comfort (Rohner, 1986, 2016). IPARTheory illuminates the
powerfully motivating effect of the emotional need for a positive response
from an attachment figure and, as such, provides a relevant and compelling
psychological roadmap to examine the maladaptive psychological and
behavioral outcomes that may occur when a child’s emotional need for
emotional security are unmet by a parent.
Perception of Parental Rejection
ACEs are comprised of parental behaviors and household dysfunctions
which a child mentally interprets and assigns meaning to (Rohner, 1986,
2016). According to IPARTheory (Rohner, 1986), the process of mental
interpretation and meaning assignment results in a child’s perceptions of
parental acceptance or rejection. For example, children whose single parent
is absent from their sports events because the parent works multiple jobs to
support the family may interpret the parent’s absence as the parent
deliberating choosing not to attend the events and, thus, as rejection. A
child’s perceptions are the bridge between a parent’s action or inaction or
some household condition and a child’s behavioral manifestation.
IPARTheory operates under three premises. First, everyone has a
biological need for love, support, comfort, and affection from others who are
important to them. Second, parental behaviors and conditions lead a child to
conclude whether they are loved and accepted. There are four categories of
these parental behaviors and conditions, each of which exists on a
continuum. Acceptance is characterized by warmth and affection. The
remaining three categories are forms of rejection: (a) hostility-aggression,
(b) indifference-neglect, and (c) undifferentiated rejection (Rohner, 1986;
2016). The third premise of IPARTheory is that people tend to respond to
perceived rejection through any of seven personality dispositions when they
conclude they are rejected: (a) anger and hostility, (b) dependence or
defensive independence, (c) negative self-esteem, (d) negative self-
adequacy, (e) emotional instability, (f) emotional unresponsiveness, and (g)
negative worldview (Rious, Cunningham, & Beale Spencer, 2019; Rohner,
2004; Rohner & Lansford, 2017).
Generally, the more rejected a child feels, the more of these
personality dispositions the child tends to adopt (Rohner, 2004, 2016). When
these seven personality dispositions form a negative stable pattern of
personality over time, the result is a condition that Rohner (2004, 2016) has
termed rejection syndrome. Not unlike the posttraumatic stress responses
demonstrated by Pavlov’s dogs (Pavlov, 1927) and Horowitz’s humans
(1976), Rohner (2004, 2016) identified a conditioned personality disposition
among children who perceived chronic parental rejection.
Although IPARTheory has not previously been applied to the study of
singleparent households and their relationship to long-term violence, it is an
appropriate framework to examine the psychological phenomena at the root
of children’s interpretation of the conditions often accompanying the
experience of growing up in a single-parent household and those that drive
behavioral outcomes, including long-term extreme violence. IPARTheory
enables the tracking of a child’s psychological perceptions of the conditions
that frequently accompany life in a single-parent household through the
behavioral manifestation of those perceptions, particularly in cases where
negative perceptions go unchallenged or unprocessed. IPARTheory uniquely
provides a theoretical explanation for a child’s path from adverse event to
cognitive interpretation to affective response to behavior, both immediate
and long-term.
Warmth and Affection
Parental acceptance is characterized by warmth and affection (Rohner,
1986, 2016). The most widely studied dimension of parenting (Rious et al.,
2019), warmth and affection refer to expressions of love, affection, support,
praise, care, empathy, guidance, and genuine interest by a parent toward a
child (Khan & Munaf, 2017). Emotional engagement with and emotional
connection to the child are foundational to parental warmth and affection
(Briere, Runtz, Eadie, Bigras, & Godbout, 2017).
Parental warmth and affection have long been recognized as critical to
the development of positive outcomes across a person’s lifespan. Parental
warmth is correlated with flourishing in midlife on psychological, emotional,
and social measures of well-being (Bethell, Gombojav, & Whitaker, 2019;
Chen, Kubzansky, & VanderWeele, 2019). Researchers have linked parental
emotional availability, a characterization of warmth and affection, with
decreased aggression in children (Babore, Carlucci, Cataldi, Phares, &
Trumello, 2017). Parental warmth is a protective factor against risky and
deviant behavior associated with perceptions of parental rejection (Daspe,
Arbel, Ramos, Shapiro, & Margolin, 2018; Denes, Bennett, & Winkler,
2017). Researchers suggest that warmth and acceptance tend to be absent in
single-parent households where the parent is overburdened with
responsibilities and/or copes poorly with these burdens (Baker, Jensen, &
Tisak, 2019; Sasser, Beekman, & Bierman, 2015).
Hostility and Aggression
Rohner (1986, 2016) described three categories of parental behaviors
and conditions that children interpret as rejecting. One is hostility-
aggression. In the context of IPARTheory, parental expressions of
animosity, anger, or resentment, leading to harmful verbal and physical
behavior (i.e., abuse) toward their children, characterize the hostility-
aggression construct (Khaleque, 2017). Abusive parental behaviors may
include verbal assaults, insults, and domineering (e.g., harsh criticism, name-
calling, screaming); physical violence toward the child; and other behaviors
that may cause physical or emotional harm to the child (Hunt, Goddard,
Cooper, Littlechild, & Wild, 2016; Khaleque & Ali, 2017; Rohner &
Lansford, 2017).
Researchers suggest that birth parents perpetrate physical and
emotional abuse of their children most commonly (Sedlak et al., 2010),
leading to various forms of externalizing problems by children and
adolescents (Glatz, Lippold, Jensen, Fosco, & Feinberg, 2019; Khaleque,
2017; Weymouth, Buehler, Zhou, & Henson, 2016). Verbal aggression by
parents has been linked to oppositional defiant disorder (Contreras & del
Carmen Cano, 2016; Derella, Burke, Stepp, & Hipwell, 2019). Parental
aggression toward children in the form of corporal punishment, including
spanking, has been linked to subsequent aggression in children (Yaros,
Lochman, & Wells, 2016), although researchers disagree as to the
consistency of this finding (Gershoff et al., 2018; Rohner & Melendez-
Rhodes, 2018). Less deliberative parental hostility and aggression, such as
the parent losing emotional control and lashing out at a child, has been more
consistently associated with early and enduring signs of anger, hostility,
aggression, delinquency, and antisocial behavior in children and adolescents
(Atherton, Conger, Ferrer, & Robins, 2016; Glatz et al., 2019; Hay,
Meldrum, Widdowson, & Piquero, 2017; Meldrum, Connolly, Flexon, &
Guerette, 2016). IPARTheory research shows significant correlation between
maternal and paternal hostility and aggression and psychological
maladjustment that manifests through any of the seven negative personality
dispositions put forth by Rohner (2004, 2016; Khaleque, 2017; Rious et al.,
2019; Rohner & Lansford, 2017).
Fosco, Lippold, and Feinberg (2014) theorized that children raised in
households where hostility and aggression are normalized become socialized
into a hostile interaction style. The development of aggressive behaviors in
children may be associated with rigid and/or inconsistent parenting
behaviors (Derella et al., 2019; Patterson, 2002; Patterson, 2016). The
child’s aggression may strengthen the parents’ negative parenting practices,
which reinforces the child’s aggression (Patterson, 2016). This reciprocal
relationship is a form of operant and classical conditioning reminiscent of
Pavlov (1927), Seligman (1972), and other behavioral researchers, in which
the child becomes conditioned over repeated parental interactions to behave
aggressively (Patterson, 2002). Once parents develop a cycle of negatively
reinforcing a child’s aggressive behavior, it may be difficult to correct, even
if the parent’s behavior changes, as conditioned behavioral patterns tend to
survive after discontinuation of the initial stimulus (Lunkenheimer,
LichtwarckAschoff, Hollenstein, Kemp, & Granic, 2016; Patterson, 2002).
Children raised in a hostile or aggressive household tend to
demonstrate a generalized hostility in public interactions. Hostility toward
peers often suggests exposure to parental hostility (de Vries et al., 2018).
Similarly, children may attribute hostile motives to others, eliciting a
defensive or aggressive response from the child (Healy, Murray, Cooper,
Hughes, & Halligan, 2015; Yaros et al., 2016).
Children raised in a hostile or aggressive household may also
demonstrate hostility or aggression toward the parent or parents (Derella et
al., 2019; Fosco et al., 2014; Martinez-Ferrer & Stattin, 2016). Researchers
suggest that child-to-parent aggression occurs more commonly in children
who perceive the parent as generally hostile and neglectful of the child’s
needs, rather than as corrective (Contreras et al., 2016; Rohner & Melendez-
Rhodes, 2019). High impulsivity, a hostile social perception, and an inability
to navigate social situations are common among children and adolescents
who aggress toward their parents (Contreras et al., 2016).
Child victims of hostility, aggression, and interpersonal violence have
a significantly increased risk for aggressive behavior and violence in
adolescence and adulthood (Heleniak & McLaughlin, 2019). The aggressive
behavior that begins in childhood and adolescence as a consequence of
parental hostility and aggression is at a markedly elevated risk of turning
into violent, sometimes serially violent, behavior throughout the child’s
lifetime (Heleniak & McLaughlin, 2019). Specifically, in singleparent
households where the sole parent is disproportionately hostile, rejecting, and
uses psychological, verbal, or physical aggression against the child, long-
term criminal offending by the child is an increased risk (DeLisi & Vaughn,
2016).
Child abuse, including hostility and aggression by parents toward their
children, is common among recurrently violent offenders, including serial
killers (Mitchell & Aamodt, 2005; Willmott, Boduszek, & Robinson, 2018).
A tragic example is Donald “Pee Wee” Gaskins, who confessed to killing
approximately 100 people but was convicted of killing eight, including
several children and a baby, in the early 1970s (Townsend, n.d.). Gaskins
was born to a poor 14-year-old alcoholic girl who prostituted herself for
money. The girl was unmarried to Gaskins’ father, who was a wealthy local
landowner who paid for sex with the girl, and who had no relationship with
Gaskins (Kirby, Wolford, & Hayward, 2011). Throughout Gaskins’
childhood, his mother had sex in front of him, and would laugh and push
him away when he tried to make her stop (Kirby et al., 2011; Townsend,
n.d.). Several of Gaskins’ mothers’ clients abused and sexually assaulted
Gaskins while his mother looked on (Kirby et al., 2011; Townsend,
n.d.). Gaskins was teased at school for his small stature and for the bruises
on his body (Crime Museum, 2017). Blaming him for his inability to get
along with his classmates, teachers repeatedly beat Gaskins. He quit school
at age 8 (Kirby et al., 2011).
Gaskins’ mother married a man who verbally and physically abused
Gaskins (Crime Museum, 2017). The beatings continued through Gaskins’
adolescence when he began to steal and engage in other delinquent behavior
(Kirby et al., 2011; Townsend, n.d.). At age 15, Gaskins participated in a
gang rape of a friend’s sister for which he was sent to reform school where
he was sodomized nightly for three years by a school leader (Crime
Museum, 2017; Kirby et al., 2011; Townsend, n.d.). Gaskins attempted
murder at age 19 when a woman threatened to turn him in for the arson of a
tobacco farm. He hit her over the head with a hammer, but the woman
survived (Kirby et al., 2011; Townsend, n.d.). In jail for his crime, Gaskins
was sexually assaulted repeatedly by fellow inmates. In an attempt to
establish his dominance, Gaskins slashed the throat of a fellow inmate,
committing his first murder at age 20 (Crime Museum, 2017; Kirby et al.,
2011; Townsend, n.d.). His series of murders, however, did not begin until
Gaskins was 36 years old. For the next six years, Gaskins claimed to have
targeted hitchhikers, both male and female, then strangled, suffocated,
stabbed, and shot his victims. After they died, Gaskins said he mutilated the
bodies and, in some cases, cannibalized them (Townsend, n.d.).
Gaskins’ story punctuates the disastrous and heartbreaking behavioral
outcomes that may occur as a consequence of prolonged, intense hostility
and aggression by a parent toward a child. Unquestionably an extreme case
of child abuse, Gaskins’ story reveals the escalation in his angry, aggressive,
and ultimately violent behavior over time and the many missed opportunities
to intervene on his behalf during Gaskins’ childhood. Many serial killers
experience hostility and aggression at the hands of their parents or other
primary caregivers, to a milder degree than Gaskins in some cases (e.g. John
Wayne Gacy, Gary Ridgeway) and comparatively severe in others (e.g.,
Henry Lee Lucas, Richard Ramirez).
Neglect and Indifference
Neglect. Child neglect, the failure to provide necessary care, is the
most common form of mistreatment reported to authorities (Gilbert et al.,
2009; U.S. Department of Health & Human Services, 2018; Vanderminden
et al., 2019). More than 1 in 17 children (6.07%) in the United States
experienced physical or emotional neglect in 2018, and more than 1 in 7
(15.14%) experienced neglect at some time in their lives (Vanderminden et
al., 2019). Neglect can be physical or emotional (Khodabandeh, Khalilzadeh,
& Hemati, 2018). Physical neglect may be described as the failure to protect
a child’s safety (Sulima, 2019), and often occurs when supervision is lacking
in the context of single parenting. Emotional neglect is “the absence of
sufficient attention, responsiveness, and protection that are appropriate to the
age and needs of a child” (National Scientific Council on the Developing
Child, 2012, p. 2). The forms of deprivation that emotional neglect may take
include, for example, chronic ignoring, dismissing, belittling, overlooking
the child’s needs, understimulation, emotional non-responsiveness, and
withholding love or emotional support (Hart, Brassard, Binggeli, &
Davidson, 2002; Khaleque & Ali, 2017).
The psychological impacts of emotional neglect to a child are
extensive. Although neglect has been identified by researchers as an
understudied ACE (Bland, Lambie, & Best, 2018; Fagan & Novak, 2018;
Widom, 2017), researchers suggest that child neglect is at least as damaging
to children as physical or sexual abuse in the longterm (Gilbert et al., 2009;
Vanderminden et al., 2019). Adverse consequences include an increased risk
of internalizing behaviors, such as depression and anxiety; and externalizing
behaviors, including aggression and delinquency; delayed or altered
cognitive and emotional development; a lack of emotional resiliency in the
short- and long-term; insecure attachment style; behavioral and personality
disorders; poor academic performance; substance abuse; risky sexual
behaviors; aggression; and violence (Bland et al., 2018; Stoltenborgh,
Bakermans-Kraenburg, & van IJzendoom, 2013; Vanderminden et al.,
2019).
Psychological effects produce behavioral consequences. Khodabaudeh
et al. (2018) identified a correlation between emotionally neglected children,
decreased selfesteem, and subsequent behavioral problems. Researchers
have found that neglect may double the likelihood of childhood behavioral
problems (Norman, Byambaa, De, Butchart, Scott, & Vos, 2012), including
elevating the risk of antisocial behavior (Braga, Gonçalves, Basto-Pereira, &
Maia, 2017) and juvenile recidivism (Ryan, Williams, & Courtney, 2013).
Research shows a direct link from neglect to physical aggression and
violence (Felitti et al., 2019) and criminal offending (Grady et al., 2016). A
longitudinal study of children ages 0 to 12 who were victims of chronic
neglect revealed impaired social functioning and predicted aggression and
delinquency at age 14 (Logan-Greene & Jones, 2015). Chronic maltreatment
including neglect of 0- to 14-year-old children predicted male delinquency at
age 21 (Abajobir et al., 2017). Khodabandeh et al. (2018) found a strong
correlation between neglect in childhood and adulthood aggression among
350 adult men criminally accused of physical aggression. Child neglect
research makes clear the deleterious effects of chronic neglect to a range of
antisocial and criminal behavior, including aggression and violence, through
a child’s lifespan.
Like child abuse, child neglect is common among recurrently violent
offenders, including serial killers (Yaksic, 2018). For example, Edmund
Kemper killed 15 people, mostly women, in the 1970s. He killed his
grandparents when he was 15 years old and later killed his mother. His
mother was a domineering alcoholic who was overly critical of her son,
berating him in public and blaming him for her divorce when he was 9 years
old (Biography.com, n.d.; Leyton, 2003). In addition to these hostile-
aggressive behaviors, Kemper’s mother forced him to sleep in the locked
basement for 8 months, purportedly so he could not harm his sisters
(Biography, n.d.; Hickey, 2016; Leyton, 2003). This neglectful behavior not
only contributed to under-stimulation, emotional nonresponsiveness, and a
failure to provide needed psychological care to Kemper by his mother, but it
suggests a history of chronic maternal neglect of Kemper’s emotional needs
such that Kemper’s aggressive behavior had reached a level where his
mother feared for the safety of his sisters. Years later, Kemper cited a
seething hatred for his mother as a reason for his murders (Leyton, 2003).
Kemper’s case demonstrates the contribution of parental neglect to a child’s
antisocial behavior and, ultimately, to recurrent long-term violence in
adulthood.
Andre Crawford was convicted of killing 11 women from 1993 to
1999. Crawford’s neglect began in his infancy, when he was abandoned in
filth and squalor. His mother admitted to leaving him for hours, even days,
while she prostituted herself. When authorities learned of his abandonment,
Crawford was put into foster care where he suffered all manner of physical
and sexual abuse, primarily by his female caretakers. He was subsequently
returned to his family, where he was forced to have sex with a family
member (Walberg, 2009). Crawford suffered horrific neglect and abuse in
his young life. His caretakers were consistently derelict in providing
Crawford’s most basic human needs for affection, positive attention,
responsiveness, safety, and protection. These experiences undoubtedly
shaped Crawford’s psychological and social development and likely fueled
the violent aggression Crawford perpetuated through his murders
(Garbarino, 2017; Su, 2018; Walberg, 2009).
Indifference. IPARTheory pairs neglect with indifference (Rohner,
1986, 2016). The seemingly less severe manifestation of neglect, parental
indifference may be characterized as uninvolved but not overtly dismissive
or rejecting parenting (Briere et al., 2017). Insensitivity, a lack of
responsiveness to a child’s emotional needs, and the absence of warmth and
affection typify parental indifference (Boyer, Scott, & Nelson, 2016; Briere
et al., 2017). Parental indifference has been described as caretaker emotional
disengagement, emotional distance, emotional unavailability, lack of
awareness of the child’s experience, inattention, distraction, misattunement,
and diminished responsiveness (Artz et al., 2016; Briere et al., 2017; Kahn &
Munaf, 2017). Parental indifference also suggests a lack of warmth,
affection, love, sympathy, or interest in the child (Khan & Munaf, 2017). In
its physical manifestation, parental indifference may involve the failure to
provide for and the lack of supervision of a child (Fagan & Novak, 2018).
The reduced temporal, cognitive, and emotional resources a single parent
may have for meaningful child interaction makes indifferent or disengaged
parenting an increased risk.
The behaviors that characterize parental indifference operate by
invalidating a child’s emotional experiences (Tanaka, Wekerle, Schmuck, &
Paglia-Boak, 2011; Vettese, Dyer, & Wekerle, 2011). Indifference
communicates to a child that his or her internal experiences do not matter
(Westphal, Leahy, Pala, & Wupperman, 2016). A child interprets and
internalizes a parent’s negative response, ignorance, and otherwise uncaring
behavior as indifference (Sulima, 2019), which is interpreted as nullifying
the importance of the child’s thoughts and feelings, and subsequently
perceived as rejection (Khan & Munaf, 2017; Sulima, 2019).
Parental indifference may be extremely detrimental to a child’s
psychological and emotional health. Some researchers posit that the
psychological impact of parental indifference to a child is more emotionally
destructive than abuse (Briere et al., 2017), reconfirming that malignant
intent and harsh treatment are not necessary for psychologically damaging
effects (Artz et al., 2016; Briere et al., 2017; Sulima, 2019). Parental
indifference is associated with emotional insecurity and poor personality
development (Mendo-Lazaro, Leon-del-Barco, Polo-del-Rio, Yuste-Tosina,
& LopezRamos, 2019); mental health conditions, such as depression
(Alenazi et al., 2019; Baek, Roberts, & Higgins, 2018) and borderline
personality disorder (Bayes, Graham, Parker, & McCraw, 2018); and
psychosis (Catalan et al., 2017; Mansueto, Palmieri, & Faravelli, 2018).
Parental indifference increases a child’s risk for maladaptive
behavioral outcomes. Indifference leads to childhood antisocial and
delinquent behavior (Mwangangi, 2019) and delinquency (Baek, Roberts, &
Higgins, 2018). Anger and depression have been found to moderate the
relationship between parental indifference and delinquency, suggesting that a
child may respond to indifference through anger or depression, either of
which may precede delinquent (Baek, Roberts, & Higgins, 2018).
Parental indifference predicts aggression (Su, 2018), criminal behavior
(Artz et al., 2016; Hesselink & Booyens, 2016), including violence
(Mumford, Liu, & Taylor, 2016; Pyle et al., 2019). The likelihood of a child
or adolescent engaging in criminal behavior may increase when parental
indifference combines with low family cohesion and physical violence in the
home (Mwangangi, 2019) or when parental indifference is mediated by a
child’s poor self-control (Baek, Nicholson, Higgins, & Losavio, 2018).
Moreover, parental indifference is predictive of violence in adolescence,
both against the self through self-harming behaviors and suicide (Chung &
Lesorogol, 2019) and against others, often through dating violence
(Mumford et al., 2016; Reyes, Foshee, Markiewitz, Chen & Ennett, 2018).
Although researchers have begun to identify the deleterious effects of
parental inattention, distraction, or lack of awareness of a child’s needs
(Briere et al., 2017), additional research is needed to more deeply understand
the long-term effects of indifferent parenting to violent behavior (Bland et
al., 2018). Research of the relationship to violence in children of a single
parent where the parent exhibits behaviors indicative of indifference may
further this understanding.
Undifferentiated Rejection
Of the three categories of parental behaviors and conditions that
children interpret as rejecting, undifferentiated rejection is the least
understood (Ali, Khatun, Khaleque, & Rohner, 2019). Undifferentiated
rejection refers to a child’s belief that a parent does not care about,
appreciate, or love the child even absent objective evidence that this
conclusion is true (Rohner, 1986, 2016). A child may interpret and
internalize a parent’s behavior as rejecting when an outside observer sees no
indication through parental behaviors or conditions of interpersonal rejection
(Ali et al., 2019; Khaleque, 2017).
Although the behavioral triggers of a child’s perception of rejection in
such cases is unclear, research underscores the damaging psychological
impacts to the child. For example, respondents worldwide reported a
significant association between the experience of undifferentiated maternal
and paternal rejection and measures of overall psychological maladjustment
in both children and adults (Ali et al., 2019). Maladjustment as a product of
undifferentiated rejection may manifest through many of the same negative
personality dispositions as parental hostility (Rious et al., 2019; Rohner,
2014; Rohner & Lansford, 2017). Despite the lack of research into
undifferentiated rejection, existing research makes clear its potentially
devastating consequences to a child, further strengthening the role of a
child’s perception of rejection to his or her long-term wellbeing.
Cognitive, Affective, and Behavioral Components
Following Rohner’s development of IPARTheory (1986), he and other
researchers sought to more deeply understand the way perceptions of
parental rejection operate by exploring the cognitive, affective, and
behavioral components of the phenomenon. Rohner (2004) hypothesized that
children draw a fundamental judgment about whether they are loved by a
parent based on the parent’s responsiveness to and support of the child. If the
child concludes he or she is unloved, this judgment contributes to the child’s
diminished feelings of self-worth and assumption of his or her unlovability
by others (Miranda, Affuso, Esposito, & Bacchini, 2016; Rohner, 2004).
IPARTheory predicts that children who perceive rejection by their parents
are likely to develop maladaptive cognitive and affective manifestations
before they act out behaviorally. These cognitive and affective
manifestations express through a common set of negative personality
dispositions and dysfunction behavior that may pervade through adulthood
(Rohner, 2004). According to IPARTheory, the trajectory from parental
indifference, to perceptions of parental rejection, to the development of core
beliefs about oneself and others, to internalized feelings and externalized
behaviors is common among people regardless of differences in culture,
ethnicity, language, gender, or race (Ali et al., 2019; Rohner, 2004).
Cognitive manifestations. On the path from an ACE to a child’s
perception of parental rejection, several internal processes occur. The first
involves a mental interpretation of the ACE in which the child assigns
meaning to the event. As part of his attachment theory, Bowlby (1973)
described the meaning-making process as the development of an internal
working model (IWM). An IWM is the cognitive framework an individual
uses to process and organize mental information, which informs one’s
understanding of and expectations about our inherent worth, basic trust in
other humans, and general worldview (DeWinter, Vaudevivere, Waters,
Braet, & Bosmans, 2016). For example, through the experience of having a
single mother who works three jobs to provide for her children, a child may
conclude that the mother does not prioritize him or her because the mother is
frequently absent, mistaking a caretaking responsibility for neglect or
indifference, and consequently may feel rejected.
According to IPARTheory, parental rejection is a developmental risk
factor and contributes to children’s negative evaluation of themselves and
their future (Miranda et al., 2016; Rohner, 2004). Because children define
their own fundamental worth based on their perceptions of parents’
emotional availability and responsiveness to their needs, a parent who is
lacking in these areas may produce a child who negatively self-evaluates
(Miranda et al., 2016; Rohner, 2004). IPARTheory further suggests the
quality of early parental experiences is internalized and incorporated within
an IWM, creating expectations for the availability and responsiveness of
people beyond the parent (Trumbell, Hibel, Mercado, & Posada, 2018). A
child who perceives a parent or other primary attachment figure is
unavailable or unresponsive to the child’s emotional needs is likely to
develop core inaccurate beliefs that others will be as or more unavailable and
unresponsive as the parent (Rohner, 1984, 2004; Smeijers et al., 2018).
Believing relationships are unsafe, the child develops heightened rejection
sensitivity through childhood and adulthood (Khaleque et al., 2019). An
expectation of hostility or indifference from others toward the child evolves,
and the child filters all perceptions of and communications with others
through this expectation (Khaleque et al., 2019; Rohner, 2004).
A child may make hostile attributions to others’ motives (Rohner,
1986, 2004; Smeijers et al., 2018). Cognitive and perceptual distortions may
occur as a result of the child’s expectation of others’ behavior as hostile and
untrustworthy. These may include personalizing, hypervigilance,
hypersensitivity, selective perceptions, and selective attention to information
that reinforces the child’s expectation of others (Rohner, 2004). Adolescents
ages 9 to 13 negatively interpreted ambiguous maternal behavior, even after
controlling for depressive mood (DeWinter et al., 2016). Similarly, parents’
physical absence impacted children’s emotional health and perceptions of
self-worth even when children were aware of the reasons for parents’
absence and when the absence was to financially support the family (Wang,
Zhang, & Chen, 2019). Both DeWinter et al. (2016) and Wang et al. (2019)
demonstrated the negative filter through which children who are denied a
parent’s emotional availability and responsiveness perceive the larger world.
Perceptions of parental rejection create and reinforce an IWM that the world
at large cannot be trusted (Bowlby, 1973; Waters, Ruiz, & Roisman, 2017).
Affective manifestations. Once an ACE has been mentally processed
as thought and meaning has been assigned to the experience, emotion arises.
Like the development of cognitive IWMs, affective manifestation is an
internalized process (Rohner, 2004, 2016). Negative self-evaluations and
negative evaluations of the future as a product of perceptions of parental
rejection make children vulnerable to depression, anxiety, and insecurity
(Briere et al., 2017; Miranda et al., 2016; Rohner, 1984, 2004). These
affective responses to rejection are universal, independent of culture,
ethnicity, race, or other demographic circumstance (Rohner, 2004, 2016).
Psychological pain from perceived parental rejection often manifests
through anger and resentment (Ali et al., 2019; Rohner & Lansford, 2017).
Because of its mediating role between parental rejection and aggression,
anger is a critical component to criminal behavior and violence (Baek et al.,
2018). Notably, however, researchers suggest that anger alone does not
correlate with a child’s long-term psychological and behavioral outcomes;
rather, the health of the relationship between parent and angry child is
determinative.
Brock and Kochanska (2019) studied anger proneness and parental
attachment security in 102 children at four points in time, from infancy
through early school age. Children were exposed to scenarios that involved
the mother leaving the child alone for a short period. Over time, some of the
children demonstrated negative emotions and oppositional behaviors while
others did not. The researchers identified the emotional attachment between
the parent and child as the critical factor in the children’s responses. Even
the children who displayed anger at the time the mother left them alone in
the research scenarios did not show anger over time unless the child was
insecurely attached to the parent. In cases where the child was insecurely
attached to the parent, the child’s initial anger at being left alone set a
trajectory for child toward greater defiance, negative affect, and oppositional
disposition throughout childhood. In cases where the child was securely
attached, no such negative downstream effects occurred (Brock &
Kochanska, 2019). These findings demonstrate the importance of the
fundamental parent-child emotional bond, or the child’s perception of the
bond, to the child’s long-term emotional health.
Behavioral Manifestation
Negative evaluations of self, others, and the future as a product of
perceptions of parental rejection facilitate externalized behavior (Rohner,
2004; Rohner & Lansford, 2017). The form the behavior takes may be
informed by a child’s ability to regulate his or her own emotions (Brumarlu,
2015; Casselman & McKenzie, 2015). Emotional selfregulation involves the
ability to change one’s own thoughts, feelings, and impulses, and to suspend
tendencies to behave in socially undesirable ways (Li, Delvecchio, Lis, Nie,
& Riso, 2015). The quality of the parent-child relationship is highly
correlated with a child’s ability to self-regulate emotion (Cooke,
Kochendorfer, Stuart-Parrigon, Koehn, & Kerns, 2019). Sensitive, flexible,
and emotionally mature caregivers who encourage a child to express a range
of emotions and who model and teach effective emotion regulation strategies
produce children who effectively self-regulate negative emotion and show
behavioral self-control (Brumarlu, 2015; Cooke et al., 2019; Li et al., 2015).
The inability to self-regulate emotion may have injurious
psychological and behavioral consequences. Insecurely attached children are
less likely than securelyattached children to effectively manage negative
emotions, openly express emotions, and alleviate their distress in healthy
ways (Brumarlu, 2015; Casselman & McKenzie, 2015; Stern & Cassidy,
2018). As a rule, the less secure the parental attachment, the less likely a
child is to effectively self-regulate emotion, and the less self-control the
child has over his or her behavior, creating a habitually reactive pattern of
behaving (Li et al., 2015). A child’s ability to effectively manage distressing
emotions as they arise is a critical moderator between perceptions of parental
rejection and positive, healthy behavioral responses.
According to IPARTheory, children often respond to perceptions of
parental rejection with anger (Rohner & Lansford, 2017). Anger may be
acted out through oppositional defiance (Smeijers et al., 2018), delinquency
(Hambrick et al., 2018), hostility (Babore et al., 2017), aggression (Miranda
et al., 2016; Smeijers et al., 2018), and other forms of externalizing behavior
(Hunt, Slack, & Berger, 2017). Further, perceptions of parental rejection in
childhood are an important predictor of childhood and adult antisocial and
criminal behavior (Farrington, 2000; Smeijers et al., 2018). Perceptions of
parental rejection have been empirically linked to violent juvenile
delinquency (Fox, Perez, Cass, Baglivio, & Epps, 2015), juvenile arrest and
reoffending (Baglivio, Wolff, Piquero, & Epps, 2015; Fagan & Novak, 2017;
Wolff & Baglivio, 2017; Wolff, Baglivio, & Piquero, 2017), adulthood
aggression (Smeijers et al., 2018), adulthood criminal offending (Craig,
Piquero, Farrington, & Ttofi, 2017), and adulthood violence (Felitti, 2019;
Lindberg & Zeid, 2018). Researchers suggest that perceptions of parental
rejection in childhood may set a trajectory toward adulthood violence
(Cameranesi, 2016).
In a study of 100 incarcerated criminals convicted of crimes including
drug trafficking, robbery, kidnapping, rape, and first-degree murder, all 100
criminals reported the experience of parental rejection in childhood (Khan &
Munaf, 2017). A significant difference was found, however, among criminal
types on the degree of parents’ emotional warmth. The most violent
criminals, those convicted of first-degree murder, reported significantly less
paternal warmth than criminals convicted of drug trafficking. Similarly,
those with a kidnapping conviction reported significantly less maternal
warmth than murder convicts. Therefore, parental rejection predicted
criminality and the degree of warmth experienced predicted degree of
violence exhibited through criminality (Khan & Munaf, 2017).
Adverse Experiences and Trauma
Trauma is a negative emotional response to single, multiple, or long-
lasting adverse events (American Psychological Association, 2020; Center
for Substance Abuse Treatment, 2014). The notion of trauma found its
beginnings in animal research in the 1920s (Koch, 2019). Pavlov’s well-
known dog experiments demonstrated the conditioning of an initially neutral
stimulus to create a conditioned stimulus. Pavlov conditioned the dogs to
salivate in anticipation of food at the sound of a buzzer or metronome by
pairing the sound with meat powder. Over time, what was initially a neutral
event, the sound of the buzzer or metronome, had been conditioned to
generate a predictably positive salivation response by the dogs (Pavlov,
1927).
Years later, Seligman (1972) expanded on Pavlov’s research to
investigate the conditioning of a negative response in dogs. Like in Pavlov’s
experiments, a dog was placed into a box with two halves, and then was
conditioned to anticipate food at the ringing of a bell. The sound of the bell
was then paired with electric shocks of varying intensity. In initial response
to the bell/shock pairing, the dog ran around, howled, defecated, and
urinated, until it realized it could jump into the other half of the box,
escaping the shocks (Seligman, 1972). Next, Seligman restrained the dog in
one half of the box, and the bell/shock pairing resumed. The dog attempted
to escape the shocks; however, recognizing it was not in control of what
happened to it, the dog cowered in the back of the box quietly until the
shocks stopped (Seligman, 1972). These neurotic responses continued even
when the restraints were removed, the shocks discontinued, and the dog was
simply presented with the sound of the bell (Seligman, 1972). The same
response occurred across multiple dogs. The phenomena of learned
helplessness became “a model for the emotional numbing and maladaptive
passivity sometimes following victimization” (Peterson & Seligman, 1983,
p. 103).
As a result of Pavlov’s experiments, he and subsequent researchers in
the Pavlovian tradition understood trauma as a conflict of psychological
forces, resulting in a disruption of the nervous system (Koch, 2019; Pavlov,
1927). On the shoulders of Pavlov’s work, researchers began to study the
traumatic impacts of adverse events on humans. Watson and Rayner (1920)
exposed a 9-month-old child called Little Albert to various stimuli, including
a white rat, rabbit, monkey, and several inanimate objects, to which Little
Albert exhibited no fear. The white rat was reintroduced to the boy, this time
pairing the rat with a loud noise, causing the child to cry. After repeated
pairings of the white rat and the loud noise, Little Albert cried after seeing
the white rat, absent the loud noise. The white rat, a previously neutral or
perhaps positive stimulus, had been conditioned to elicit a fear-based
response in the child (Watson & Rayner, 1920). Thereafter, Little Albert
cried in response to similar white furry objects, such as a white fur coat and
Santa’s beard (Watson & Rayner, 1920). Despite the unethical nature of the
experiments on Little Albert (Cornwell & Hobbs, 1976), the experiments
produced two valuable findings: emotional responses may be conditioned in
humans, and those conditioned emotional responses are generalizable to
other similar stimuli (Watson & Rayner, 1920).
Building on this body of research into conditioning and trauma
responses, Horowitz (1976) found that, like Seligman’s (1972) dogs, humans
attempt to avoid unpleasant experiences through thought suppression,
emotion suppression, and avoidance of stimuli associated with the trauma
(Horowitz, Wilner, & Alvarez, 1979). When those experiences prove
unavoidable, humans develop various trauma responses such as anxiety,
irritability, restlessness, and fatigue (APA, 2020). This and similar trauma
research ultimately led to recognition of post-traumatic stress in humans not
as indicative of a weak biological or emotional constitution, but of a
legitimate psychiatric disorder (Bortolon & Raffard, 2019; Koch, 2019).
Post-traumatic stress disorder (PTSD) was introduced as a psychiatric
diagnosis in the third edition of the Diagnostic and Statistical Manual of
Mental Disorders in 1980 (American Psychiatric Association, 1980).
Contemporary researchers developed a new understanding of trauma,
not as a battle of internal forces, as Pavlov (1927) proposed, but a
consequence of a lack of control over one’s circumstances (Koch, 2019;
Seligman, 1972). This paradigm reflects “changed societal concerns that
entailed a transformation of the vision of how individuals relate to
threatening environments and social forces beyond their control” (Koch,
2019, p. 3). This paradigm shift is consistent with modern research literature
regarding children’s maladaptive responses to frequent, long-term, or intense
exposure to inescapable adverse experiences.
Single-Parent Household as an Adverse Childhood Experience
ACEs refer to any abuse, neglect, or other traumatic exposure that
occurs before age 18 (CDC, n.d.; Fagan & Novak, 2018; Felitti et al., 2019;
Karatekin & Hill, 2019) that often lead to negative long-term psychological
consequences (Boullier & Blair, 2018). ACEs may include household
dysfunction that behaviorally manifests through, or is psychologically
interpreted by a child as, abuse or neglect (Fagan & Novak, 2018; Felitti et
al., 2019). Examples of household dysfunction may include, for example,
parental absence, parental substance abuse, and financial hardship. ACEs
commonly cooccur, increasing the likelihood of negative short- and long-
term outcomes in children and adults (Hunt, Slack, & Berger, 2017).
Because of their prevalence and destructive long-term consequences, ACEs
have been labeled a public health crisis (Grady, Levenson, & Bolder, 2016).
Researchers suggest that ACEs set a trajectory toward deleterious life-
persistent outcomes. Frequent or intense childhood adversity often leads to
psychological and emotional trauma, which negatively impacts normal
psychological and social development over time (Garbarino, 2017; Grady et
al., 2016). If a child does not have a strong attachment to a parent, various
adverse outcomes may occur (Lindberg et al., 2018). These include
depression and anxiety (Alenazi et al., 2019; Briere et al., 2017);
preadolescent and adolescent delinquent behavior, including violent
delinquency (Abajobir et al., 2017; Hambrick, Rubens, Brawner, & Taussig,
2017); juvenile offending (Wolff & Baglivio, 2017; Wolff, Baglivio, &
Piquero, 2017) and violent criminal offending into and throughout adulthood
(Craig, Piquero, Farrington, & Ttofi, 2017; Smeijers et al., 2018). The
correlation between ACEs and adverse outcomes, including criminal
behavior and violence, are well-established (Lindberg et al., 2018).
Maladaptive Outcomes
A single-parent household may expose a child to ACEs in multiple
ways. Children living in a single-parent household experience the
psychological effects of the absence of the parent who has left the
household. Many children of single parents are poorly supervised, increasing
their exposure to experiences they are emotionally unequipped to handle or
allowing others inappropriate access to a child (Ben-David, 2016). A single
parent who copes ineffectively with the burdens of responsibility may
respond to a child using unduly harsh tactics or by emotionally withdrawing
from the child, perhaps leaving the child to draw inaccurate conclusions
about his or her self-worth (Jackson et al., 2019; Theobald, Farrington, &
Piquero, 2013). Growing up in a singleparent home may increase a child’s
vulnerability for abuse, neglect, and indifferent treatment by the single
parent (Afifi et al., 2015; Mathews & Abrahams, 2018). Each of these ACEs
may influence a child’s psychological development.
Researchers have identified multiple maladaptive psychological and
behavioral outcomes associated with single-parent households. Children who
grow up with a single parent are at elevated risk for psychological distress
(Clements-Noelle & Waddington, 2019; Sinha & Ram, 2019), obesity
(Gardner, Feely, Layte, Williams, & McGavock, 2019), sexual activity and
pregnancy at an early age (Vazquez-Nava et al., 2019), grade retention in
school (Hinojosa et al., 2019), poor social skills (Nawaz et al., 2019),
adverse peer relationships (Gioumouki, Smaili, Antoniou, & Babalis, 2018),
and delinquency (Burlaka, 2016; Dijanic, 2016). Growing up in a single-
parent household is related to inhibited impulse control, poor planning
ability, poor problem-solving, and unwanted, intrusive thoughts (Doebel &
Zelazo, 2016). Children of single parents may receive less emotional support
than children with two in-home parents (Maschi, Schwalbe, & Ristow,
2013), making these children more likely to leave home at an early age (van
den Berg, Kalmijn, & Leopold, 2018).
Single-parent household is predictive of the negative long-term
psychological states and behavioral outcomes that lead to and encompass
serial killing. Growing up in a single-parent home is associated with anger in
children that, without intervention, may become a stable personality trait
(Dijanic, 2016). Poorly regulated anger may manifest as relational
aggression, through which another’s reputation or social status is denigrated
(Baker, Jensen, & Tisak, 2019) and physical aggression (Fomby, Goode, &
Mollborn, 2016; Woods, Menna, & McAndrew, 2017), often persistent
throughout the child’s lifetime (Dijanic, 2016; Ostrov, Murray-Close,
Godleski, & Hart, 2013).
Violence is strongly associated with single-parent households
beginning in childhood (Fergusson et al., 2007; Mok et al., 2018; Sattler &
Thomas, 2016). Children and adolescents who grow up in a single-parent
home are at increased risk for gang affiliation (Pyrooz & Sweeten, 2015) and
violence toward the parent (Fegadel & Heide, 2018; Gabriel et al., 2018).
One study found that child-to-parent violence occurs in almost 20% of
single-parent homes (Armstrong et al., 2018). Researchers suggest that
violent behavior that begins in childhood may endure through adulthood
(Fergusson et al., 2007).
The rate of single-parent households has steadily increased since 1960
(Beaulieu & Messner, 2010) and risen more significantly since 1990
(Coulton et al., 2018). As of 2019, more than one-quarter of preschool-age
children were living in single-parent households (Baker, Jensen, & Tisak,
2019). The prevalence of children living in singleparent homes and the
potentially deleterious effects of a single-parent home to children’s long-
term well-being makes it critical to understand the role of a single parent in a
child instigating and perpetrating the most extreme forms of violence
(Mathews & Abrahams, 2018; Paluch et al., 2019).
Contributors
Parental absence. Children raised in single-parent homes necessarily
experience the absence of a parent. Although children and adolescents raised
by one parent reported higher overall life satisfaction than those raised by
non-parental caregivers, research shows that emotional support from both
parents is optimal for positive child and adolescent development (Costa,
Sireno, Larcan, & Cuzzocrea, 2019; Hayles, Xu, & Edwards, 2018;
McCarty, Zimmerman, Digiuseppe, & Christakis, 2005). According to a
study by Hayles et al. (2018), high school aged adolescents who reside with
both parents are significantly more satisfied with their lives than children
who are raised by one parent, grandparents, or other caretakers. This result
held regardless of the adolescents’ feeling of connectedness with their
caregivers, demonstrating the importance of parental connection to a child’s
well-being.
Permanent absence. In all single-parent scenarios, one of a child’s
two biological parents is absent from the home. A parent is permanently
absent if there is no contact with the child or if the parent is deceased
(Trujillo & Servaty-Seib, 2018). Permanent parental absence can be
psychologically devastating to a child, increasing the risk of adverse
psychological and behavioral outcomes (Johnson, Torres, Sykes, Gibson, &
Baker, 2017). Children exposed to permanent parental absence are five times
more likely to engage in self-harm and suicide than children who have not
experienced parental absence (Trujillo & Servaty-Seib, 2018). Fatherless
boys are at greater risk for joining violent gangs than boys whose father is
present (Stewart, 2018). Permanent parental absence is associated with
elevated risk for subsequent violent offending, particularly when the absence
begins in early childhood and when the mother is the absent parent (Mok et
al., 2018).
Temporary absence. Alternatively, parental absence can be
temporary. In the context of single-parent families, a child whose parent is
involved in the child’s life but does not reside full-time with the child
experiences this form of parental absence. Regardless of parental intent,
temporary parental absence may be internalized by a child as neglect or
indifference (Khaleque, 2017; Sulima, 2019). Research is clear that
temporary absence of a parent predicts maladjustment in children and
adolescence through adulthood. In a field study of 346 children and
adolescents, 173 separated parents, and 173 intact parents, researchers
assessed the effects of parental separation from the child on the child’s well-
being. Psychological effects of temporary separation from a parent included
depression, anxiety, hostility, lack of impulse-control, social withdrawal,
decreased self-esteem, paranoid ideation, interpersonal alienation, and
decreased self- and family-concept (Seijo, Fariña, Corras, Novo, & Arce,
2016). Outwardly measurable negative outcomes included increased
probability of poverty, decreased academic performance, increased school
drop-out rates, and increased exposure to gender violence.
Significant research confirms the relationship between temporary
parental absence and criminal behavior. A myriad of studies have tied
criminal behavior and violence in adolescence and adulthood to temporary
parental absence due to work demands (Dittman, 2018), migration for work
(Beazley, Butt, & Ball, 2018; Sulima, 2019; Zhang, Zhang, & Ding, 2019),
military deployment (Dittman, 2018; Gewirtz & Zhang, 2018), incarceration
(Giordano, Copp, Manning, & Longmore, 2019; Haney, 2018; Muftić, &
Smith, 2018; Schwartz-Soicher, Geller, & Garfinkel, 2011; Wakefield &
Wildeman, 2014), and other forms of temporary parental absence (Artz et
al., 2016; Hayles, Xu, & Edwards, 2018). The body of research on the long-
term psychological and behavioral impacts of parental absence strongly
suggests that children perceive rejection from parental absence, regardless of
the purpose or length of the absence, in some cases evolving into adulthood
violence.
Poor parental coping. Single parenthood is often tremendously
stressful for the single parent (Gioumouki et al., 2018). Unassisted
caregiving, burdensome financial responsibilities, and decreased social
support relative to two-parent households lend to various manifestations of
psychological distress among single parents (Rousou et al., 2019). Single
parents frequently report feelings of loneliness (Gioumouki et al., 2018),
depression (Hernandez, Aranda, & Ramirez, 2009; Jackson et al., 2019), and
anxiety (Theobald et al., 2013). Economic hardship often plagues single
parent households (Coulton et al., 2018; Manjunatha et al., 2019).
Poor coping skills by single parents may limit their ability to
effectively manage their life circumstances and, as a consequence, their
emotions. The high rate of child murders perpetuated by single parents is an
extreme illustration of the inability to effectively manage one’s own mental
health (Dekel et al., 2018). More commonly, single parents cope with mental
and emotional distress in less extreme but potentially damaging ways.
Problem drinking, alcoholism, and drug abuse, often used to cope with
difficult circumstances, are associated with single parenthood (Kong &
Easton, 2018; Manjunatha et al., 2019). Unmanaged frustration may
contribute to domestic violence between parent and child or between parent
and non-relative men (Kong & Easton, 2018; Zerr et al., 2019).
A parent’s inability to emotionally self-regulate may contribute to
poor quality parenting behaviors, including harsh and inconsistent behavior
toward children (Mathews & Abrahams, 2018; Shaffer & Obradovic, 2017).
Researchers suggest that single parents tend to cope through punitive
behaviors and disciplinary tactics to gain a child’s compliance (Briggs et al.,
2016). In a longitudinal study of children ages 6 to 15 years, child aggression
contributed to parenting stress, instigating further harsh parenting behaviors
and creating a negative reciprocal pattern (Briggs et al., 2016; Krahe et al.,
2015).
In other cases, single parents may emotionally withdraw from children
in response to oppressive demands. Children of parents who are physically
present but emotionally absent are at increased risk for antisocial and
criminal behavior (Artz et al., 2016; Hesselink & Booyens, 2016). Sulima
(2019) found that poor quality parenting characterized by parental
disengagement, lack of affection and support, and inconsistent discipline
predicted aggression and juvenile delinquency. This research provides
evidence of the effects to children of limited cognitive and emotional
resources a single parent may have to invest in a child as a function of poor
coping skills.
Lack of parental supervision. Children of single parents are often
left unsupervised by an adult while the single parent is at work, attending to
other children or responsibilities, or coping with depression, substance
abuse, or other affliction. Lack of parental supervision during periods of
parental absence contributes to negative child development outcomes
(Vanderminden et al., 2019). For example, insufficiently supervised children
are at highest risk for sexual victimization by a non-family adult (Turner et
al., 2019), substance abuse in adolescence (Caspi, Lardier, & Barrios, 2018),
and juvenile delinquency (Sulima, 2019).
Researchers have long recognized supervisory neglect as the most
common form of child neglect and that supervisory neglect is associated
with criminal behavior (Farrington, 1996; Vanderminden et al., 2019). The
decrease in the incidence of supervisory neglect among children who live
with both biological parents and the increase in trauma, substance abuse, and
suicidal ideation among children who experience supervisory neglect implies
a psychological impact to the child beyond excessive freedom to engage in
potentially destructive behavior that a lack of supervision may invite.
Children who experience physical and supervisory neglect may suffer the
most trauma (Turner et al., 2019), setting a trajectory for delinquency,
recidivism, and in the most extreme cases, violent criminal behavior (Pyle et
al., 2019).
Abuse and neglect. As a consequence of a single-parent’s
burdensome responsibilities and potentially poor coping skills, children in
single-parent households are more likely to experience physical and
emotional abuse and neglect than children living with coupled parents (Afifi
et al., 2015; Gross-Manos et al., 2019). Strikingly, over half of children in
single-parent households have been involved in some form of abuse or
substantiated neglect (Afifi et al., 2015). Abuse and neglect rates for children
in singleparent households are especially high where poverty and financial
hardship exist (Briere, 2019; Pyle, Flower, Williams, & Fall, 2019; Taliep,
Ismail, & Titi, 2018; Vreeland et al., 2019). The relationship between child
neglect and poverty is stronger than any other type of child maltreatment
(Widom, 2017).
Just as children who grow up in single-parent households are at
increased risk for abuse, neglect, and exposure to various dysfunctional
household conditions, these children are vulnerable to the associated adverse
short- and long-term emotional and behavioral outcomes (Costa et al., 2019;
Gross-Manos et al., 2019; Vanderminden et al., 2019). Investigating the
relationship between single-parent households and child, adolescent, and
adulthood violence through a psychological framework may help illuminate
the role of single-parent households in the commission of recurrent, long-
term violence.
Effect of the Single-Parent Household on Serial Killing
Serial Killers
Despite continuing public interest in serial killers, empirically-based
information is somewhat limited (Hodgkinson, Prins, & Stuart-Bennett,
2017). Public understanding of modern serial killers is largely driven by
media portrayals, which tend to represent serial killers as monsters (e.g.,
Jeffrey Dahmer) or celebrities (e.g., Ted Bundy) (Wiest, 2016). Walters,
Drislane, Hickey and Patrick (2014) published a summary of pervasive
myths about serial killers. These include, among others, that serial killers are
white men who are intelligent, psychopaths, sexually motivated, target
strangers, highly mobile, kill alone, use brutal methods, have high body
counts, and struggle between a compulsion to continue killing and a deeper
desire to get caught (Walters et al., 2014).
Research contradicts many of these highly reductionist
generalizations. Although many serial killers are solo white men who are
sexually motivated, many are not. At least one in five, and possibly more,
serial killers are black (Hickey, 2016; Walters et al., 2014). Nearly 17% are
women (Hickey, 2016; Walters et al., 2014). Up to 25% of serial killers have
a partner with whom they commit homicides (Fox & Levin, 2011; Hickey,
2016). Most serial killers are average or below average intelligence (Hickey,
2016; Leary, Southard, & Aamodt, 2019; Walters et al., 2014). Many serial
killers are married or in stable long-term relationships, employed, and
commit homicides within a local area (Hickey, 2016; Walters et al., 2014).
While some serial killers are psychopaths, a significant number do not
qualify as a psychopath based on the PCL-R psychopathy checklist (Hickey,
2016; Walters et al., 2014). Victims of serial killers are not always strangers
(Hodgkinson et al., 2017; Prins, 2015), nor are they necessarily young white
women (Hickey, 2016; Miller, 2014; Walters et al., 2014). Some serial
killers target minorities or children, or have no demographically-focused
victim (Hickey, 2016; Miller, 2014). Most, but not all, serial killers tend to
victimize individuals of the same race as the killer (Miller, 2014).
A serial killer’s motive is frequently fantasy-based. Approximately
two-thirds of serial killers are sexual sadists in which the offender acts out a
fantasy by inflicting torment on the victim (Hickey, 2016). In these cases,
the victim is merely a prop for the offender’s motivation to achieve sexual
gratification by acting out the fantasy (Hickey, 2016; Miller, 2014). Not all
serial killers are pleasure-oriented, however; some are purpose-oriented
(Miller, 2014). Serial killers may be motivated by delusion (e.g., to rid the
world of undesirable people, such as prostitutes) or power over the helpless
(e.g., to kill elderly, children, or disabled people in their care or custody). In
other cases, serial killers may be motivated by utilitarian reasons, such as to
achieve financial gain, to enact revenge (Hickey, 2016; Miller, 2014).
Serial killers are an extremely violent population; however,
demographic and psychological characteristic vary widely within the
population. Serial killers are not frequently monstrous cannibals who engage
in necrophilia, nor are they charismatic, handsome, and cunning gentlemen
(Wiest, 2016). An accurate understanding of serial killers’ wide-ranging
physical and demographic characteristics, personalities, backgrounds,
motivations, and victim preferences is important to ensure findings from the
study of serial killers are properly contextualized and interpreted. It is with
the perspective that serial killers are not a dichotomous group but a highly
diverse population with the perpetration of multiple homicides in common
that we should seek to understand the relationship between the
circumstances of serial killers’ upbringing and the scale of their violence.
Scale of Violence
Although researchers associate growing up in a single-parent
household with violent behavior across the child’s lifespan, there is
significantly less research on the scale of violence that a single-parent
childhood may evoke. Scale and severity of violence are terms often used
interchangeably in the research literature (Marshall, 1992; Harris, Oakley, &
Picchioni, 2013; Troisi, 2018; Tyrer et al., 2007). Efforts to quantify
violence severity sometimes include measures of degree (Tyrer et al., 2007).
This approach has been criticized, however, as subjective and error-prone.
Bowers (1999) encouraged researchers to use objective, behavioral
components of violence to determine severity.
Assessing the frequency of various facets of violence is a common
method of measuring violence severity because of its objective nature
(Harris, Oakley, & Picchioni, 2013). More than half of nine tools designed to
assess violent behavior reviewed by Harris, Oakley, & Picchioni (2013)
included frequency, or number of instances of a behavior, as a measure of
the scale of violence. Because of its relative measurement objectivity, I will
use frequency and duration, a method of measurement similar to frequency
in its numerical objectivity, to quantify the scale of homicidal violence.
Measures of scale in the context of serial homicide will include the number
of victims suspected, the number of victims confessed to, the number of
victims convicted of having killed, and the duration of violent homicidal
behavior. Each of these measures speaks to the extent to which an individual
perpetrates violence over time.
Summary
Researchers have established an escalatory trajectory from ACEs
associated with single-parent households to a host of negative long-term
outcomes, including criminal behavior and violence (Mok et al., 2018;
Sattler & Thomas, 2016). Although research on the role of IPARTheory
within the context of single-parent households is limited, existing research
on IPARTheory strongly supports the notion that ACEs commensurate with
growing up in a single-parent home, when interpreted by a child as rejection,
predicts significant short- and long-term maladaptive behavioral outcomes.
In the most extreme cases, a child may respond with recurrent homicidal
violence beginning at an early age and continuing throughout his or her
lifespan.
Although research has revealed a link between a single-parent
upbringing and long-term violence, there has been little investigation of the
scale of violence associated with growing up in a single-parent household.
IPARTheory provides an appropriate psychological framework by which to
examine the relationship between a single-parent upbringing and the scale of
long-term violence operationalized through serial homicide. This analysis
may deepen our understanding of the magnitude of the psychological
influence that growing up in a single-parent household may have on
children.
Chapter 3: Research Method
Introduction
The purpose of this study was to examine the scale of violence
associated with a single-parent upbringing. Prior research has established the
correlation between growing up in a single-parent household and long-term
violent behavior (Fergusson et al., 2007; Theobald et al., 2013). This study
expands on the existing research by dissecting the scale of violence
associated with a single-parent upbringing. Solo, male serial killers, an
inherently violent population, were the subjects of study.
In this chapter, I present a detailed overview of the research design
and rationale and the components of the methodology, which includes the
population, sampling procedures, data collection procedures,
instrumentalization and operationalization of constructs, and data analysis
plan. I discuss potential threats to validity. Finally, I discuss the ethical
procedures I followed in conducting the study, including attaining the
approval of the Walden University Institutional Review Board (IRB).
Research Design and Rationale
I used a quantitative research design to perform a cross-sectional study
using archival data. Cross-sectional designs enable the comparison of two
preexisting groups of people based on the presence or absence of the
independent variable (Mann, 2003). The research design includes one
categorical independent variable with two levels for comparison: offenders
raised by both birth parents and offenders raised by a single parent. There
are four interval-level dependent variables: (a) the number of victims
suspected, (b) the number of victims confessed to, (c) the number of victims
convicted of having killed, and (d) the duration of violent homicidal
behavior. I chose a quantitative design to enable comparison between the
two levels of the independent variable across the four dependent variables,
expressing the comparison result numerically and categorically (Smith,
1983).
The research design was chosen with the intent of responding to the
following research questions:
RQ1: Does growing up in a single-parent household predict the
number of victims solo male serial killers are suspected to have killed?
RQ2: Does growing up in a single-parent household predict the
number of victims solo male serial killers confess to killing?
RQ3: Does growing up in a single-parent household predict the
number of victims solo male serial killers are convicted of killing?
RQ4: Does growing up in a single-parent household predict the
duration of homicide perpetration among solo male serial killers?
The research is nonexperimental using archival data contained in the
Radford/FGCU Serial Killer Database (Aamodt, 2015). Academic
researchers collaboratively established the Radford/FGCU Serial Killers
Database for the express purpose of research (Boyne, 2014; Yaksic, 2015). It
is the largest nongovernmental database of known serial killers with over
5,200 individuals and over 175 variables (Aamodt & Leary, n.d.). The large
size of the database allows for random sampling, high statistical power, and
parameter restriction without undue sacrifice of sensitivity or specificity
(Yaksic, 2015).
Methodology
Population
The sample population is convicted male serial killers listed in the
Radford/FGCU Serial Killer Database who perpetrated at least one of their
homicides in the United States and who killed their victims alone (without a
partner). Among this sample population, all serial killers who were raised by
a single parent, as indicated by the applicable variable in the database, were
included in the study. This sample population, n = 85, represent one level of
the independent variable. An equivalent number of serial killers who were
raised by both birth parents were included, comprising the population of the
second level of the independent variable. In total, 170 male serial killers
were included in the study.
Sampling and Sampling Procedures
A purposive sampling strategy was used to identify solo male serial
killers who committed one or more of their homicides in the United States in
the Radford/FGCU Serial Killer Database. From that sample population,
purposive sampling was used to identify serial killers who were raised in a
single-parent home. Purposive sampling is a type of nonprobability sampling
useful in selecting research participants who fall within a particular domain
of interest (Tongco, 2007). After filtering the sample population for serial
killers who were raised by both birth parents, these serial killers were
randomly chosen using a random number calculator (Fowler, 2014), as there
are more serial killers raised by both birth parents than by a single parent.
Each comparison group had an equal number of serial killers (n = 85).
Only those offenders who are specifically designated in the
Radford/FGCU Serial Killer Database as having been raised by the birth
mother or by the birth father were included in the study. Excluded were data
that required any assumptions or guesswork on my part as to whether or for
how long offenders grew up in a single-parent household. For instance,
offenders who may have grown up with a single parent for some period but
are designated in the database as having lived with a birth and a stepparent
were excluded. Also excluded were offenders raised by a stepparent only.
Although these offenders experienced a single primary caregiver, the
stepparent is not biologically related to the child. Because research suggests
biological relatedness may positively impact the parent-child relationship
(Fallesen & Gahler, 2019; Upreti & Sharma, 2018), these offenders were
excluded.
Selection of power (1- β) and significance level (α). I conducted a
power analysis prior to data analysis to determine the minimum appropriate
sample size for my study. I used the statistical power analysis calculator
G*Power 3.1.9.4, which was designed for use in social and behavioral
research (Faul, Erdfelder, Lang, & Buchner, 2007). With a statistical
significance level of α = .05, an alpha level commonly used in research
(Lakens, 2013), and power of 1- β = .8 (Kim, 2016), the G*Power
calculation yielded a minimum total sample size of 128 participants, or 64 in
each comparison group. My sample size exceeded the minimum necessary to
achieve power.
Effect size f2(V). To determine the effect of any difference between
the means of the two comparison groups, partial eta squared was used to
standardize the effect size. Partial eta squared is the default effect size
measured reported by SPSS when performing the multivariate analysis of
variance (MANOVA) and the analysis of variance (ANOVA) statistical tests
(Lakens, 2013). Effects were interpreted according to partial eta squared
descriptive guidelines: 0.1 = small effect, 0.6 = medium effect, and 0.14 =
large effect.
Data Collection
Radford/FGCU Serial Killer Database. All data used in the study
were included in the Radford/FGCU Serial Killer Database (Aamodt, 2015).
These archival data have been collected over more than 20 years—first by a
faculty member and his students at Radford University and eventually as a
compilation of data collected by multiple serial killer researchers. As of
April 2020, the evolving database included over 5,200 serial killers and
14,643 victims (Aamodt, Hargrove, & Witzig, 2019).
Researchers disagree as to the definition of a serial killer (Reid, 2016).
In 2005, the FBI modified the definition of a serial killer from an offender
who has unlawfully killed three or more victims in separate events to one
who has unlawfully killed two or more victims in separate events (FBI,
2005). To enable researchers to determine which definition to use, the
Radford/FGCU Serial Killer Database includes offenders who have killed
two or more victims with the option to filter the data for a higher threshold.
Excluded from the database are double murders (two murders in the same
location within a 24-hour period), triple murders (three murders in the same
location within a 24-hour period), and mass murders (four or more murders
in the same location within a 24-hour period), and spree-one event-one day
murders (two or more murders occurring in different locations within a 24-
hour period) (Aamodt et al., 2019). Spree killers (two or more murders over
a period of multiple days with no cooling off period or clear break between
kills) are included (Aamodt et al., 2019).
Only publicly available information was included in the
Radford/FGCU Serial Killer Database by Radford University researchers.
Sources include online prison records; online state birth, death, marriage,
and divorce records; online social security information; individual-level
census data; journal articles; newspaper articles; books; dissertations and
theses; and internet sources (Aamodt et al., 2019). Where inconsistent data
between data sources occurred, researchers relied on the most official
sources (e.g., death certificate rather than a media article) (Aamodt et al.,
2019).
Radford University researchers took precautions to ensure the
accuracy of information in the database. When possible, multiple sources
were used to verify each piece of information. Graduate students at Florida
Gulf Coast University, the database custodian, reviewed many of the data
fields to corroborate and source the information. Victim information was
corroborated by information in the supplementary homicide reports as part
of a joint project with the Murder Accountability Project (Aamodt et al.,
2019). Further, researchers granted access to the database must agree to
notify appropriate Radford University or FGCU personnel of any errors in
the database or new information to add to the database (Aamodt et al., 2019).
Over the years, additional researchers have contributed their findings to the
database.
Gaining access to the data set. Researchers may request access to the
Radford/FGCU Serial Killer Database through an online application process.
Access is generally granted so long as the researcher agrees not the share the
data or use it for commercial or “inappropriate” purposes (Aamodt et al.,
2019, p. 1). Researchers must agree to properly cite the database and to share
any additional relevant data the researcher gathers so it may be added to the
database (Aamodt et al., 2019). Access to the database is free of charge.
I did not complete the online application to gain access to the
Radford/FGCU Serial Killer Database. I directly contacted Dr. Michael
Aamodt of Radford University. After I agreed to the terms of use via email
(Appendix B), Dr. Aamodt provided me with the database in Excel format.
The Excel file includes the data set and codebook.
Instrumentation and Operationalization of Constructs
As discussed, the research used previously collected data contained in
the Radford/FGCU Serial Killer Database (Aamodt, 2015). The basis for
development of the database was the lack of robust sources for empirical
serial killer research, which hampered the ability to systematically research
serial homicide (Yaksic, 2016). Because I am using archival data, I did not
use a data collection instrument.
Through my research I explored two primary constructs: single-parent
households and scale of violence. Single-parent households are
operationalized as those in which one biological mother or father resides
with the child under the age of 18 (APA, 2019). By comparison, the
traditional nuclear family is one in which a child lives with both birth parents
(APA, 2019). Together, the single-parent household and the household in
which two birth parents reside comprised two levels of the independent
variable.
Scale of violence was measured through four dependent variables: (a)
the number of victims suspected, (b) the number of victims confessed to, (c)
the number of victims convicted of having killed, and (d) the duration of
violent homicidal behavior. Frequency of homicidal behavior, as measured
here by the number of victims suspected, the number of victims confessed
to, the number of victims convicted of having killed, and the duration of
homicidal behavior are readily found in the literature to measure the scale,
magnitude, or extent of some phenomenon (Blanchet et al., 2016; Harris et
al., 2013; Salamon et al., 2014). Therefore, they were used as a measure of
scale in the current study.
Data Analysis
Before analyzing the data, I performed necessary data cleaning
procedures. Missing data required to respond to the research questions were
minimal and, thus, were imputed to be included in the analysis. The research
questions and hypotheses in this study are as follows:
RQ1: Does growing up in a single-parent household predict the
number of victims solo male serial killers are suspected to have killed?
H 01: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are suspected of killing.
H a1: Growing up in a single-parent household does predict the number
of victims solo male serial killers are suspected of killing.
RQ2: Does growing up in a single-parent household predict the
number of victims solo male serial killers confess to killing?
H 02: Growing up in a single-parent household does not predict the
number of victims solo male serial killers confess to killing.
H a2: Growing up in a single-parent household does predict the
number of victims solo male serial killers confess to killing.
RQ3: Does growing up in a single-parent household predict the
number of victims solo male serial killers are convicted of killing?
H 03: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are convicted of killing.
H a3: Growing up in a single-parent household does predict the
number of victims solo male serial killers are convicted of killing.
RQ4: Does growing up in a single-parent household predict the
duration of homicide perpetration among solo male serial killers?
H 04: Growing up in a single-parent household does not predict the
duration of homicide perpetration among solo male serial killers.
H a4: Growing up in a single-parent household does predict the
duration of homicide perpetration among solo male serial killers.
Using SPSS Version 25, I performed a multivariate analysis of
variance (MANOVA) to examine the difference between two levels of the
independent variable across three dependent variables (Faul et al., 2009).
MANOVA is commonly used to test the strength between variables when
multiple dependent variables are being examined
(Zientek & Thompson, 2009). Use of MANOVA is preferable to conducting
multiple ANOVAs where, as here, more than one dependent variable is
examined for two reasons: conducting multiple ANOVAs increases the
likelihood of committing a Type I error
(Fish, 1988; Russell, 2014) and (b) multiple ANOVAs are unable to reveal
whether each level of the independent variable is related to some
combination of dependent variables or to a single dependent variable
(Russell, 2014). To control Type I error while assessing the potential
interaction between and among dependent variables, I conducted a
MANOVA. My analysis plan was to perform ANOVAs on each dependent
variable if the MANOVA test was significant at the α = .05 level to ascertain
which dependent variables or combination of dependent variables
contributed to the overall effect.
Threats to Validity
External Validity
A threat to the external validity of this study is the inclusion only of
male serial killers who committed homicides by themselves. Further, only
those who committed one or more homicides in the United States were
included. This methodological choice was made to increase generalizability
across solo male serial killers in the United States, as this demographic
comprises the greatest proportion of known serial killers (Hickey, 2016). It
may decrease generalizability of the findings across serial killers not
included in this study, such as women, serial killers who commit their crimes
with a partner or in a group, and serial killers who kill outside of the United
States, as they may be influenced by cultural considerations different from
those in the United States.
Internal Validity
The covert nature of serial homicide presents a threat to the internal
validity of this study. Because serial killers generally seek to avoid
identification and apprehension for their crimes, they may not be
forthcoming about the number of victims suspected, the number of victims
confessed to, the number of victims convicted of having killed, and the
duration of violent homicidal behavior. Therefore, because the available data
is based on arrests, confessions, and convictions, it is possible, perhaps
likely, that the data reflecting the dependent variables is erroneously
conservative. Barring wrongful convictions, the serial killers included in the
study may have committed more homicides than reported. This did not
necessarily hamper correlations between the independent and dependent
variables, but there was a risk it may decrease the strength of the dependent
variables.
Methodological issues may have threatened the validity of this study.
The data collection procedures for the portion of the Radford/FGCU Serial
Killer Database that were compiled by faculty and students at Radford
University have been described; however, there is no description of the data
collection procedures of the multiple researchers who have subsequently
contributed their data to the database. Who collected the data, the procedures
by which it was collected, the variables that were being explored, how those
variables were operationalized, and other methodological issues are
unknown. The lack of clarity about the integrity of these researchers’ data
may threaten the validity of my study.
Construct Validity
If the primary researchers were deficient in their methodological rigor
or if methodology differed across researchers who studied similar constructs,
the data used in this study was confounded. An example of inconsistent
methodology across researchers is the difference in construct definition as it
related to my independent variable. Researcher A may have operationalized
an offender’s childhood household as “birth mother,” “birth father,” “birth
parent and stepparent,” etcetera, while Researcher B may have
operationalized the same construct as “living with family.” I chose to include
only those serial killers who were clearly delineated as growing up with birth
mother or birth father. This purposive sampling strategy, however, may have
excluded from the sample serial offenders who were not included in
Researcher A’s study but were included in Researcher B’s study and who
lived with a single parent but were not specifically designated as so by the
primary researcher. The negative affect to generalizability should be
minimal provided an appropriate sample size.
Ethical Procedures
I abided by the ethical principles required by the American
Psychological Association and Walden University in the performance of my
study. To ensure the ethical soundness of my study, I sought and received
approval from the Walden University IRB (approval number 03-03-20-
0663360). Although I used archival data that is publicly available and/or has
been the subject of prior research, only includes individuals who have been
convicted of a crime, and excludes names or other personally identifying
information, the study involved human subjects. None of the data is
anonymous or confidential; however, as part of my data access agreement, I
did not share the data. I did not conduct data collection and data analysis
prior to receiving IRB approval for my study.
Summary
In this chapter, I discussed the quantitative, cross-sectional design of
my study to examine the relationship between a single-parent upbringing and
scale of long-term violence. I described the framework of the study as
including one categorical independent variable with two levels and three
interval-level dependent variables. I described the Radford/FGCU Serial
Killer database and the means by which I acquired it. I outlined the
procedure I used to identify the sample population within the database and
the combination of purposive and random sampling strategies I employed. I
discussed the operationalization of the constructs I measured and the
statistical analysis I performed to respond to my research questions. Finally,
I set forth the threats to the validity of my findings and the procedure I
underwent to ensure my study complies with the ethical treatment of human
subjects.
Chapter 4: Results
Introduction
Researchers have established a significant increase in the risk of
violent behavior across a lifetime by offenders who were raised in single-
parent homes (Fergusson et al., 2007; Heleniak & McLaughlin, 2019).
Parenting quality—as defined by measures of physical presence (Ben-David,
2016; Mok et al., 2018), emotional availability (Babore et al., 2017), and
disciplinary style (Khaleque, 2017)—may be compromised as a result of
competing demands on single parents, contributing to negative short- and
long-term psychological and behavioral outcomes, including recurrent,
extreme forms of violence, such as serial homicide (Heleniak &
McLaughlin, 2019). Although a single-parent upbringing may predict
violence, it remains unexplored whether a single-parent upbringing predicts
the scale of that violence.
In this study, I examine the scale of violence correlated with a single-
parent household upbringing by comparing measures of four variables
between serial killers raised by a single parent and serial killers raised by
both birth parents. The four dependent variables are (a) number of suspected
victims, (b) number of victims confessed to, (c) number of victims convicted
of, and (d) duration of killing. The research questions and hypotheses are as
follows:
RQ1: Does growing up in a single-parent household predict the
number of victims solo male serial killers are suspected to have killed?
H 01: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are suspected of killing.
H a1: Growing up in a single-parent household does predict the number
of victims solo male serial killers are suspected of killing.
RQ2: Does growing up in a single-parent household predict the
number of victims solo male serial killers confess to killing?
H 02: Growing up in a single-parent household does not predict the
number of victims solo male serial killers confess to killing.
H a2: Growing up in a single-parent household does predict the
number of victims solo male serial killers confess to killing.
RQ3: Does growing up in a single-parent household predict the
number of victims solo male serial killers are convicted of killing?
H 03: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are convicted of killing.
H a3: Growing up in a single-parent household does predict the
number of victims solo male serial killers are convicted of killing.
RQ4: Does growing up in a single-parent household predict the
duration of homicide perpetration among solo male serial killers?
H 04: Growing up in a single-parent household does not predict the
duration of homicide perpetration among solo male serial killers.
H a4: Growing up in a single-parent household does predict the
duration of homicide perpetration among solo male serial killers.
In Chapter 4, I will discuss the findings of the statistical analyses I
performed in response to the research questions. I will describe the data
collection, the demographic features of the sample, and the results of the
tests of the research questions regarding the impact of parental upbringing on
measures of violence frequency and duration. Finally, I will briefly
summarize the statistical findings.
Data Collection
Following approval of my study by the Walden University’s
Institutional Review Board (approval number 03-03-20-0663360), I began
data collection. The Radford/FGCU Serial Killer Database was formatted in
an Excel document. I filtered the 5,071 serial killers in the database to
include only male, solo serial killers who operated in the United States. Of
the 5,071 serial killers, 4,510 (89%) are male, 3,838 (76%) acted alone, and
3,427 (68%) operated in the United States. After filtering for these three
variables, 2,361 serial killers remained.
To identify which serial killers were raised by a single parent, I
examined a variable labeled raised. Only 701 (30%) of the 2,361 male, solo,
U.S. serial killers in the database include information on upbringing. I
selected those who were raised by birth mother only (n = 78) or birth father
only (n = 7), for a total of 85 serial killers.
Next, I selected those of the 2,361 male, solo, U.S. serial killers who
were labeled as having been raised by both birth parents. This resulted in a
list of 425 serial killers. To narrow the number of serial killers raised by both
birth parents (n = 425) to equal the number of serial killers raised by a single
parent (n = 85), I used a random number generator to select 85 of the 425
serial killers raised by both birth parents. Specifically, I used a free random
number generator at www.numbergenerator.org, selecting the serial killers
associated with the first 85 random numbers generated. Table 1 shows the
difference in racial makeup of the two groups of male serial killers. Tables 2
and 3 show each category of male serial killers’ age at first kill and known
number of victims killed, both of which are supplementary measures of
violence scale.
Table 1
Racial Makeup of Two Groups of Male Serial Killers
Upbringing White Non-White Black Hispanic Asian
Single parent 43 42 35 7 0
Both birth parents 58 27 21 5 1
Table 2
Age of First Kill by Two Groups of Male Serial Killers
Upbringing Minimum Maximum Average Median
Single parent 14 60 25.28 25
Both birth parents 13 59 28.74 26
Table 3
Number of Victims Killed
by T
wo Groups of
Ma
le Serial
Killers
Upbringing Minimum Maximum Average Median
Single parent 2 37 3.95 3
Both birth parents 2 46 5.58 3
I identified the four dependent variables in the database. For both
categories of the independent variable (upbringing by a single parent and
both birth parents), I filtered each dependent variable independently. Data
were present among all 85 serial killers for three of the four dependent
variables. Five of the 85 serial killers raised by a single parent and three of
the 85 serial killers raised by both birth parents were missing data in the
number of victims confessed to variable. Using Little’s (1988) missing at
completely random test, I found that the missing values were insignificant (p
= .595), indicating the values are missing at random. Therefore, I replaced
the missing values with predicted values (Hamilton, Ko, Richards, & Hall,
2010).
Results
Descriptive Statistics
I calculated descriptive statistics to distinguish the two groups of male
serial killers, those raised by a single parent and those raised by both birth
parents, across the four measures of violence scale. Table 4 shows the
descriptive statistics for each of the four dependent variables as they relate to
the two levels of the independent variable. The mean and standard deviation
of each dependent variable show a skew.
Table 4
Descriptive Statistics for Measures of Violence Scale
Group Mean SD N
DV1 1 5.64 5.797 85
2 5.59 6.920 85
Total 5.62 6.365 170
DV2 1 4.00 6.469 85
2 4.77 10.374 85
Total 4.38 8.628 170
DV3 1 3.60 3.767 85
2 3.13 4.498 85
Total 3.37 4.143 170
DV4 1 7.35 8.077 85
2 6.86 7.596 85
Total 7.11 7.821 170
Analysis of Assumptions
A MANOVA is a multivariate test used to determine whether the two
levels of the independent variable statistically differ on the composite of the
four dependent variables. The MANOVA requires several assumptions about
the data. First, the dependent variables must be measured at the interval or
ratio level. The dependent variables in this study are continuous, satisfying
this assumption. Second, the independent variable should consist of two or
more categorical, independent groups. The dependent variables in this study
satisfy this assumption. Third, the observations should be independent. The
offenders in one group of the independent variable are independent from
those in the other group of the independent variable; therefore, this
assumption is satisfied. Fourth, an adequate sample size is required. The test
of power indicates a sufficient sample size in each group of the independent
variable; therefore, this assumption is satisfied.
There should be no univariate or multivariate outliers in the data. To
test for multivariate outliers, I performed a Mahalanobis distance calculation.
The maximum value for the Mahalanobis distance calculation was 70.419,
larger than the critical value of 9.488 when using four dependent variables
with 95% confidence, indicating the presence of outliers (De Maesschalck,
Jouan-Rimbaud, & Massart, 2000). The assumption that there are no outliers
in the data was violated.
The Shapiro-Wilk test of multivariate normality indicated that the
distribution was non-normal for all measures of violence scale. As shown in
Table 5, the data are skewed right across all four dependent variables (p
< .05). Kurtosis was also assessed. As set forth in Table 6, all four dependent
variables show leptokurtic characteristics. Although the data were non-
normally distributed, violating the normality assumption, it is generally
accepted to use non-normally distributed data to perform statistical analyses
using a MANOVA (Tabachnick, Fidell, & Ullman, 2007).
Table 5
Test of Normality for Measures of Violence Scale
Kilmogorov-Smirnov Shapiro-
Wilk
Group Statistic df Sig. Statistic df Sig.
DV1 1 .268 85 .000 .622 85 .000
2 .302 85 .000 .492 85 .000
DV2 1 .270 85 .000 .653 85 .000
2 .322 85 .000 .449 85 .000
DV3 1 .280 85 .000 .595 85 .000
2 .306 85 .000 .479 85 .000
DV4 1 .198 85 .000 .824 85 .000
2 .188 85 .000 .831 85 .000
Table 6
Central Tendency of Measures of Violence Scale
Group Mean Median SD Skewness Kurtosis
DV1 1 5.64 4.0 5.797 3.249 12.967
2 5.59 3.0 6.920 4.353 21.897
DV2 1 5.62 2.0 6.365 2.490 6.461
2 4.00 2.0 6.469 4.143 17.967
DV3 1 4.77 2.0 10.374 4.226 24.637
2 4.38 2.0 8.628 5.592 39.160
DV4 1 3.60 4.0 3.767 1.306 1.038
2 3.13 4.0 4.498 1.425 1.895
To test the assumption of linearity, I created a scatterplot. Figure 6
illustrates the lack of linear relationship among the four dependent variables
across each level of the independent variable. If the data were linear, they
would be graphed in a straight line (Casson, 2014). Instead, the scatterplot
shows data clustered in a non-linear pattern across the dependent variables in
each group.
To test the assumption of variance-covariance matrices, I calculated
Box’s M test of equality of covariance. As shown in Table 7, the
homogeneity of covariance was greater than .001, meeting the assumption of
equal variances (Box, 1953). Thus, the observed covariance matrices of the
dependent variables are equal across the two groups of male serial killers.
Table 7
Box’s M Test of Equality of Covariance
Box’s M 28.267
F 2.754
df1 10
df2 134935.458
Sig. .002
To test the assumption of no multicollinearity, the final assumption of
a
MANOVA, I used a Pearson correlation coefficient. Table 8 shows that none
of the four dependent variables are multicollinear (r > .9) (Allison, 2012).
Moreover, there is a relationship among the variables (r > .2). The
assumption of no multicollinearity is met.
Table 8
Pearson’s Correlation Coefficient for Measures of Violence Scale
DV1 DV2 DV3 DV4
DV1 Pearson Corr. 1 .629** .671** .134
Sig. (2-tailed) .000 .000 .081
N 170 170 170 170
DV2 Pearson Corr. .629** 1 .500** .104
Sig. (2-tailed) .000 .000 .178
N 170 170 170 170
DV3 Pearson Corr. .671** .500** 1 .164*
Sig. (2-tailed) .000 .000 .033
N 170 170 170 170
DV4 Pearson Corr. .134 .104 .164* 1
Sig. (2-tailed) .081 .178 .033
N 170 170 170 170
Note. **correlation is significant at the 0.01 level (2-tailed); *correlation is
significant at the 0.05 level (2-tailed).
MANOVA
I conducted a MANOVA at an α level of .05 and a confidence interval
= .95 to determine whether a significant difference between the male serial
killer groups was present across the composite of the four measures of
violence scale. Because not all of the assumptions of the MANOVA were
met, I analyzed the results using Pillai’s Trace. There were no significant
differences between the groups on the composite of dependent variables, V =
.989, F(4, 165) = .465, p = .761 (see Table 9). The partial eta squared
analysis revealed a small effect size, and observed power was weak. Because
no significant difference was found between male serial killers raised in a
single parent home and male serial killers raised by two birth parents across
measures of violence scale using Pillai’s Trace, further tests to determine the
effect of each measure of violence scale between the groups of male serial
killers was unjustified. Therefore, post hoc tests and separate ANOVAs for
each dependent variable were not conducted.
Table 9
MANOVA for Measures of Violence Scale
Effect Valu
e
F Hypothesi
s
df
Error
df
Sig. Partial
Eta
Square
d
Noncent.
Paramete
r
Observe
d
Powerb
Pillai’
s
Trace
.011 .465a4.000 165.00
0
.76
1
.011 1.860 .158
a. Exact statistic
b. Computed using α = .05
Based on the MANOVA test results, I failed to reject the null
hypothesis for each of the four research questions, as follows:
RQ1: Does growing up in a single-parent household predict the
number of victims solo male serial killers are suspected to have killed?
H 01: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are suspected of killing.
H a1: Growing up in a single-parent household does predict the number
of victims solo male serial killers are suspected of killing.
RQ2: Does growing up in a single-parent household predict the
number of victims solo male serial killers confess to killing?
H 02: Growing up in a single-parent household does not predict the
number of victims solo male serial killers confess to killing.
H a2: Growing up in a single-parent household does predict the
number of victims solo male serial killers confess to killing.
RQ3: Does growing up in a single-parent household predict the
number of victims solo male serial killers are convicted of killing?
H 03: Growing up in a single-parent household does not predict the
number of victims solo male serial killers are convicted of killing.
H a3: Growing up in a single-parent household does predict the
number of victims solo male serial killers are convicted of killing.
RQ4: Does growing up in a single-parent household predict the
duration of homicide perpetration among solo male serial killers?
H 04: Growing up in a single-parent household does not predict the
duration of homicide perpetration among solo male serial killers.
H a4: Growing up in a single-parent household does predict the
duration of homicide perpetration among solo male serial killers.
Summary
The purpose of this quantitative cross-sectional study was to examine
the scale of violence correlated with a single-parent upbringing. The results
for all four research questions based on the MANOVA indicated no
statistically significant differences between the two groups of the
independent variable: male, solo, U.S. serial killers raised in single-parent
homes and those raised with both birth parents. Parental composition of the
offender’s childhood household did not predict the number of victims an
offender was suspected of killing, confessed to killing, nor convicted of
killing. Moreover, parental composition of the offender’s childhood
household did not predict the duration of killing.
The null hypotheses could not be rejected. Given the lack of statistical
significance of the MANOVA, I did not conduct post hoc tests.
In Chapter 5, I discuss the implications of the results. I address
limitations of the study and offer recommendations for social change. I
conclude the chapter by suggesting future research based on the results of
my study.
Chapter 5: Discussion, Conclusions, and Recommendations
Introduction
The quest to understand the contributors to extreme, recurrent, long-
term violent behavior has inspired research into childhood influences.
Researchers have established significant links between ACEs and negative
psychological and behavioral outcomes in the short and long term (Kratsky
& Schroder-Abe, 2018; Paluch et al., 2019). A singleparent upbringing is
among the childhood influences studied, as growing up with a single parent
may both be an ACE in itself, such as the adverse psychological impacts of
an absentee parent (Trujillo & Servaty-Seib, 2018), and invite additional
ACEs, such as poverty, lack of supervision, and parental depression (Afifi et
al., 2015; Mathews & Abrahams, 2018). Temporal and financial resource
limitations and increased demands on single parents contribute to a
vulnerability in children of single parents to conditions that foster anger,
aggression, and long-term violent behavior (Mathews & Abrahams, 2018;
Sulima, 2019).
Although research strongly correlates a single-parent upbringing with
short- and long-term maladaptive behavioral outcomes, including violence,
there has been less study of the scale of those outcomes (Heleniak &
McLaughlin, 2019). To address this understudied area, I examined the scale
of the violence correlated with a single-parent upbringing. Specifically, I
examined large-scale violence, as measured by variables of frequency and
duration, among male serial killers, an inherently violent group of
individuals. Notably, the study did not simply test the relative scale of
violence among criminal offenders, but among serial killers, arguably the
most violent offenders in society. Male serial killers with a single-parent
upbringing were compared with male serial killers raised by both birth
parents on measures of frequency and duration of homicides to determine
whether male serial killers raised by a single parent tend to perpetuate more
homicides and over a longer period of time than male serial killers raised by
both birth parents. In short, I examined indicators of extreme violence
among the already extremely violent. For a correlation to be significant, a
single-parent upbringing must predict not simply violence or even homicidal
violence, but the highest frequency and duration of homicidal violence.
After identifying two equal-size groups of male serial killers from the
Radford/FGCU Serial Killer Database—one group comprised of male serial
killers raised by single parents and the other raised by both birth parents—I
compared the groups on several measures. I performed a comparison of
racial makeup between the groups and comparisons of age at first kill and
known number of victims killed, both supplementary measures of violence
scale. I analyzed the descriptive statistics for each group of male serial
killers across the four measures of violence scale. I discussed the statistical
analyses of the various assumptions about the data that must be met for a
MANOVA. Finally, I discussed the results of the MANOVA and the reasons
post hoc tests were unnecessary. The results and my recommendations based
on them may offer guidance for future research on this topic.
Interpretation of the Findings
Parenting quality is predictive of a child’s long-term psychological
well-being and behavior (Mathews & Abrahams, 2018; Sulima, 2019).
Researchers have distinguished between single-parent households and those
in which two birth parents are present in terms of parenting quality, noting
that, as a rule, children raised with both birth parents enjoy greater parenting
quality, face fewer ACEs, and are more socially adaptive in both the short
and long term (Fallesen & Gahler, 2019; Upreti & Sharma, 2018). Children
who suffer from poor quality parenting, including but not limited to hostility,
abuse, neglect, and indifference, are at greater risk for a host of maladaptive
outcomes, including longterm violent behavior (Heleniak & McLaughlin,
2019). This line of research served as the context for my study.
A clear racial divide was revealed through a comparison of the racial
makeup of the groups. Male serial killers raised by a single parent were split
nearly evenly between Whites and non-Whites. By contrast, White male
serial killers more than doubled nonWhite male serial killers among those
raised by both birth parents. This finding is consistent with contemporary
research indicating that Whites are more likely than non-Whites to grow up
with both birth parents in the home (Chetty, Hendren, Jones, & Porter, 2018;
Raley, Sweeney, & Wondra, 2015).
Although not a measure of violence scale in this study, examination of
a male serial killer’s age the first time he commits a homicide may help
underscore the factors relevant in the offender’s life at the time the
homicidal behavior began. Both groups of offenders began to kill in their
mid-20s. There were differences in the average age of homicidal onset
between groups, with male serial killers raised by a single parent starting to
kill at just over 25 years old, while male serial killers raised by two birth
parents did not start killing until nearly 29 years old. The median ages,
however, were 25 and 26, respectively, suggesting older age outliers among
serial killers raised by two birth parents. The minimum and maximum ages
of onset were remarkably similar between groups. The youngest raised by a
single parent was 14 years old, and the youngest raised by two birth parents
was 13 years old. Similarly, the oldest raised by a single parent was 60 years
old, and the oldest raised by two birth parents was 59 years old.
The data distribution between groups on the measure of total number
of victims killed through independent homicides provides another layer of
insight. The minimum number of victims of male serial killers raised by a
single parent and those raised by two birth parents was two. Given that two
is the low threshold of independent homicides required to be categorized a
serial killer under the current definition (FBI, 2005) and the statistical
likelihood that a relatively large number of male serial killers would fall into
the low threshold, it is unsurprising that the two groups have this in
common. Similarly, the median number of victims through separate
homicides was three for both groups. Three is a relatively low number of
homicides for a serial killer given that two is the low threshold and, from a
statistical perspective, is an unsurprising finding. Unexpected was the
difference in the maximum number of victims through independent
homicides between groups. The maximum number of victims by a male
serial killer raised by a single parent was 37, while the maximum by a male
serial killer raised by two birth parents was 46. This high volume of victims
by a male serial killer raised by two birth parents skewed the average. Male
serial killers with a single parent averaged nearly four victims while those
with two birth parents in the household averaged over 5.5 victims.
The data distribution of both groups across all four measures of
violence scale was skewed right. That is, the majority of suspected,
confessed, and convicted homicides were relatively low with few high
outliers. Approximately 80% of all sampled male serial killers were
suspected of killing no more than six people. The mean number of suspected
victims by male serial killers raised by a single parent was only slightly
higher than the mean of those raised in a two birth parent home; however,
the standard deviation of the two birth parent group was larger, suggesting
the male serial killers suspected of killing a large number of victims were
from the two birth parent group.
The measure of confessions was particularly skewed. Approximately
70% of male serial killers across both groups did not confess to a homicide
or confessed to no more than two homicides. The mean number of
confessions was 4.4, with a relatively large standard deviation between
groups of 8.6. Although skew and kurtosis is evident, particularly in the first
three dependent variables, they were greatest among the data for
confessions. This suggests that, most of the time, the studied sample of male
serial killers did not confess, but when they did, they tended to confess to a
large number of homicides. As with suspected homicides, male serial killers
raised by two birth parents made the largest number of confessions.
The average number of homicide convictions across both groups was
over three, with a large concentration between two and three, and the
remaining portion dispersed upward. Male serial killers with a single-parent
upbringing received slightly more homicide convictions than those raised by
two birth parents. Again, however, the high outliers were those raised by two
birth parents.
The duration of homicides averaged just over seven years across
groups; however, over one-third of male serial killers’ homicidal stint lasted
less than one year. Male serial killers raised by a single parent tended to
continue killing for a longer duration than male serial killers raised by two
birth parents. Further, the cases in which a serial killer continued
perpetrating homicides for decades tended to be those raised in a single
parent household.
Most, but not all, of the assumptions for MANOVA existed. As
discussed, for both groups of male serial killers, the data across each of the
measures of violence scale were non-normally distributed, contained
outliers, and were non-linear. These assumption violations may have
impacted the results. The MANOVA showed no significant difference
between the male serial killer groups across the composite of the four
measures of violence scale. In other words, when the four measures of
violence scale were combined into a single measure of violence scale and
compared between the two groups of male serial killers, each group’s
measures of violence scale were not statistically different from the other
group. Had the MANOVA yielded a significant difference, I would have
performed additional tests to determine on which measure(s) of violence
scale the groups differed. However, because the MANOVA showed no
statistical difference between groups on the composite of the four measures
of violence scale, I concluded that in comparison to male serial killers raised
by two birth parents, male serial killers raised by a single parent do not differ
significantly in the number of victims they are suspected of killing, the
number of victims they confess to killing, the number of victims they are
convicted of killing, and the duration of their serial killing.
I was unable to reject the null hypotheses for each of the four research
questions. These findings should be interpreted cautiously, however, to
prevent overextending their implications. Although the results did not
support a conclusion that growing up in a single-parent home or a two birth
parent home predict violence scale as the construct was measured here, it
would be incorrect to conclude that the parental constitution of the childhood
home does not predict violence scale. Rather, through this study, I failed to
demonstrate the correlation between the parental constitution of the home
and violence scale.
Theoretical Explanation
The theoretical framework for my study is IPARTheory (Rohner,
1986), which holds that the process of mental interpretation and meaning
assignment results in a child’s perceptions of parental acceptance or
rejection. As a general premise, the more ACEs a child experiences as a
result of a parent’s behavior or conditions established by a parent, the more
rejected a child feels. In turn, the more negative thoughts and feelings about
himself and others, personality dispositions, and behaviors the child will
tend to adopt over time (Rohner, 1986; 2016).
Given the statistically insignificant results of the study, it is logical to
conclude that a single-parent upbringing, at least in isolation, does not
contribute to large-scale serial homicide through adulthood any more than
being raised by two birth parents. A conclusion informed by IPARTheory
may be that a child raised in a single-parent household may not perceive
parental rejection significantly more than a child raised by both birth parents.
This suggests it is not the parental composition of the household in and of
itself that contributes to the ACEs a child may perceive as rejecting. Rather,
the impetus of the negative cognitions, affect, and behavioral outcomes may
be more nuanced than simply who raises the child. Although research clearly
shows that ACEs frequently accompany a single-parent upbringing, this does
not preclude the ACEs that may exist in a two birth parent home. Abuse,
neglect, lack of supervision, poverty, drug abuse, and mental health issues
exist in many homes where two birth parents are present (Behere, Basnet, &
Campbell, 2017). Therefore, a deeper dive into the specific components of
the single-parent and two birth parent homes may be necessary to more
clearly understand the factors that trigger the trajectory from ACEs to a
child’s perceptions of rejection, to the development of cognitive models,
affective responses, and behavioral responses as described by IPARTheory.
Limitations
The present study successfully fulfilled its primary purpose: to
examine the scale of violence correlated with a single-parent upbringing.
There were, however, several limitations and methodological weaknesses
that may have affected the results and the generalizability of the results. For
instance, I examined only one potential contributor to long-term violence
scale: the parental constitution of a male serial killer’s childhood home.
Research makes clear that family structure may act as a proxy for various
environmental determinants of crime, including but not limited to poverty,
substance abuse, and exposure to delinquent peers (Goldstein et al., 2019).
Still, large-scale violence is likely a result of complex and multilayered
combination of factors. Although a single-parent upbringing is itself an ACE
(Pitkanen, Remes, & Moustgaard, 2019) and tends to invite other ACEs, a
single-parent upbringing may not, in isolation, predict the most frequent and
prolonged homicidal violence examined here. It may be that a singleparent
upbringing operates in combination with other factors not measured in this
study. An exploration of mediating variables may reveal a more significant
though indirect relationship between a single-parent upbringing and long-
term large-scale violence.
Another potential limitation of my research was the lack of analysis
into the specific conditions of the two birth parent cases. Research has long
held that growing up with two birth parents is most psychologically
beneficial (Behere, Basnet, & Campbell, 2017; Fallesen & Gahler, 2019;
Upreti & Sharma, 2018). However, households where two birth parents are
present are not immune from dysfunction (Behere, Basnet, & Campbell,
2017; Sedlak et al., 2010). The cases of two birth parents in this study may
have included domestic violence, parent-child conflict, sexual abuse, lack of
emotional support, lack of parent involvement, substance abuse, poverty,
lack of supervision, or other ACE. Single-parent homes are not inherently
more traumatic to children than two birth parent homes; single-parent homes
simply present a greater risk factor for ACEs (Behere, Basnet, & Campbell,
2017). Without exploring the specific conditions of the two birth parent
households, we cannot know for certain that the children raised in them had
fewer ACEs. Without controlling for these household conditions, we cannot
confidently ascertain the relative effects of single parent and two birth parent
homes on violence scale.
Within the construct of parental structure, I examined only two
possibilities: single parent and two birth parents. There are many other
parental structures that I did not examine, such as a birth parent and a step-
parent, a step-parent as single parent, a birth parent and a live-in significant
other, grandparents, foster parents, and others. It may be that the study of
multiple parental structure variations would help to illuminate the variables
related to household structure that are most predictive of long-term large-
scale violence.
In addition to the potential limitations of the independent variable,
there may be limitations to the dependent variables. The measures of
violence scale used in this study may not have been ideal measures of that
construct. Although research supports the use of frequency and duration of a
particular behavior as evidence of its scale or magnitude (Harris, Oakley, &
Picchioni, 2013), the measures of frequency and duration used in this study
had limitations. For example, the number of victims a male serial killer is
suspected of, confessed to, and convicted of killing in the selected cases are
dependent on the serial killers being found out. It is likely, perhaps certain,
that there are male serial killers who are never apprehended. A recent
estimate of unsolved serial homicides is approximately 2,000 (Pappas,
2018). If a portion of these unsolved serial homicides were perpetuated by
offenders raised in a single-family home, the study sample may have largely
changed. The absence of data on these male serial killers may impact the
findings.
Even among those male serial killers who are identified, the number of
a male serial killer’s victims and the duration of his homicides are highly
dependent on how quickly law enforcement identifies and apprehends him.
A well-resourced law enforcement agency may catch a killer quickly while a
poorly resourced law enforcement agency may not. This has no bearing on
the killer’s characteristics, including the conditions of his upbringing, but
has everything to do with the circumstances of the jurisdiction in which he
committed his crimes. Because the measures of violence scale are highly
influenced by variables not accounted for in this study, the results may be
confounded.
A potential methodological weakness of the study was the data set.
Because I used archival data collected and labeled by other researchers, I am
unable to validate its accuracy. There may be variation across researchers as
to the definition of a single-parent upbringing where, perhaps, one researcher
may have identified a case as a single-parent upbringing only if the absent
birth parent never lived in the home, while another researcher may have
labeled a case as a single-parent upbringing if, for any portion of the child’s
upbringing, he was raised by a single parent. These are different scenarios
that may produce different psychological and behavioral outcomes.
Another limitation of the present study is the sample size. Although
the data set is comprised of over 5,200 serial killers, only 85 were male,
acted without a partner, perpetuated at least some of their crimes in the
United States, and were raised by a single parent. This is due, in part, to the
relatively few serial killers for whom there is information in the
Radford/FGCU Serial Killer Database about the parental structure of their
childhood homes. Only 701 (30%) of the 2361 male, solo, U.S. serial killers
contained in the database included information about who raised the
offender. A larger sample size may have yielded more significant results.
Alternatively, a larger sample would have increased the confidence level of
the validity of my results.
An additional limitation of the study is the generalizability of the
findings. I chose to focus my population to male and solo serial killers, the
most common types of serial killers (Hickey, 2016), and to those whose
crimes were committed, at least in part, in the United States. These choices
were made to improve the generalizability of the results across serial killers
within the same demographic group. Assuming generalizability to other
male, solo, U.S. serial killers from a statistical perspective, the findings may
not be generalizable to serial killers who fall outside of these categories.
Female serial killers, those who commit homicides with a partner or in a
group, and those who operate outside the United States may be influenced by
different psychological, social, and cultural factors. For this reason, findings
based on male solo serial killers operating in the United
States should not be generalized to these different groups.
Recommendations
The limitations and methodological weaknesses of my study lend to
recommendations for future research. My study may be repeated after
performing additional research into the childhood family structure of
additional male serial killers, increasing the sample size and, therefore,
enabling greater confidence in the study’s results. In response to the
potentially over-simplistic relationship between a single-parent upbringing
and scale of violence, future researchers may dissect the relationship more
fully. For example, a researcher may focus on the role of mediating variables
in the studied relationship. Alternatively, a researcher may delve more
deeply into the adverse conditions that made up the single-parent and two
birth parent households in my study. Deeper analysis into the ACEs found in
both groups may provide greater insight into root factors of behavioral
differences. Additional variations of parent structure may be included in
future research, such as a birth parent and a step-parent, a single step-parent,
grandparents, and others. Future researchers may reveal particular household
structures beyond the single-parent household that lend to comparatively
larger-scale violence.
Rather than study an extremely violent population like male serial
killers, future research may explore the relationship between a single-parent
upbringing and a less extremely violent population. Examples may include
single homicide perpetrators, domestic violence offenders, sexual violence
perpetrators, or other groups of offenders who have committed assault or
battery. Removing the extreme nature of the population’s behavior may yield
more significant results.
The measures of violence scale used in my study may be modified to
better align with the construct of violence scale in future research. Rather
than using measures of frequency and duration, which are significantly
impacted by external influences, perhaps measures of intensity, such as
overkill, mutilation, or evidence of torture, may be used to measure violence
scale. By assessing the relationship between a single-parent upbringing and
violence scale using different and perhaps more precise dependent variables,
more significant results may emerge.
In addition to refining and expanding research of male solo serial
killers who committed homicides in the United States from single-parent
homes, future research may focus on serial killers having demographic
characteristics different from those included in my study. These may include
female serial killers, serial killers who committed homicides with a partner
or in a team, and serial killers who operated in other countries besides the
United States. These groups may be compared within themselves on the
relationship between a single-parent upbringing and violence scale.
Alternatively, the influence of a single-parent upbringing in one or more of
these groups may be compared to the influence of a single-parent upbringing
among male, solo serial killers in the United States. Using the
Radford/FGCU Serial Killer Database, future researchers may combine
variable in myriad ways to further examine the long-term effects of a
singleparent upbringing across serial killers of multiple characteristics.
Further, I recommend that future research into the role of a single-
parent upbringing and long-term violence scale employ IPARTheory as a
framework for examination. IPARTheory offers an explanation for a child’s
cognitive, emotional, and behavioral response to events and conditions
stemming, directly or indirectly, from a parent’s decisions and behaviors.
Highlighting the role of a child’s subjective perceptions of parental
acceptance and rejection as the impetus for a child’s personal map of the
world, including his own worth, the trustworthiness of others, and the value
of other human lives, and how this map informs all subsequent beliefs and
behaviors may provide powerful insight into the path from childhood ACEs
to large-scale violence throughout adulthood.
Implications
Children who grow up in a single-parent household are at elevated risk
for longterm violent behavior (Fergusson et al., 2007; Theobald et al., 2013).
Previous researchers indicate this relationship is a function of the exposure
to ACEs that children raised by a single parent commonly experience
(Jackson et al., 2019; Manjunatha et al., 2019; Rousou et al., 2019). My
study expanded on these research findings in two ways: it included only a
violent population, and it and compared those raised in a single-parent
household with those raised by two birth parents to assess whether a single-
parent upbringing was correlated with greater frequency and duration of
violence.
The results of my study showed no significant relationship between a
singleparent upbringing and measures of violence scale among the inherently
violent population of male serial killers. Notwithstanding the limitations and
weaknesses of the study, the implication of the results is that a single-parent
upbringing, in isolation, is not determinative of the scale of violence an
individual may display where scale of violence is assessed through measures
of frequency and duration. There was no statistically significant evidence
that growing up with a single parent predicted more frequent or longer
lasting episodes of killing than growing up with two birth parents. In both
groups of male serial killers, some killed twice while other killed dozens of
times. If fact, in the majority of sampled cases, the male serial killers with
greatest number of victims grew up with both birth parents in the home.
Similarly, male serial killers from both groups killed for less than a year
while other killed for decades. No correlation could be drawn from these
outcomes to the parental constitution of the offender’s childhood home.
To the extent that the parental structure of the childhood home is
related to a male serial killer’s violence scale, these results imply there are
more foundational factors at play. In the context of previous research on the
topic, these results seem to highlight the point that it may not necessarily be
the number of parental figures in a child’s home that is dispositive of the
number or strength of the ACEs the child will experience or, perhaps more
importantly, the way a child will interpret and respond to those ACEs.
Rather, the quality of the emotional acceptance and support the parent or
parents provide a child through support in navigating these ACEs may be a
more determinative factor in longterm behavioral outcomes. From the
perspective of IPARTheory, a child’s perceptions of acceptance or rejection
of an event or condition are highly dependent on the emotional support a
parent provides to a child in the face of the event or condition (Rohner,
1986; 2016).
From a social change perspective, these findings contribute to the
development of a fuller, more precise narrative about the role of a single-
parent upbringing in long-term violence. A single-parent upbringing may be
an overly broad predictor of violence scale. The narrative should reflect not
simply the parental structure of the childhood in the prediction of large-scale
long-term violence, but a more granular evaluation of the present parent’s
role in providing a child with the emotional foundation to manage whatever
ACEs may come. IPARTheory may be an effective lens through which to
understand parents’ role in directing a child’s interpretation of and response
to adverse events and conditions, changing the child’s trajectory away from
antisocial and violent outcomes.
These findings have implications for social workers, child and family
psychologists, teachers, courts of law, and other social entities charged with
the protection of children. Although a single-parent upbringing is a risk
factor for negative psychological and behavioral outcomes, we should be
cautious not to overestimate the potential scale of these outcomes based on
the parental conditions of a child’s upbringing alone. This is particularly true
when retrospectively assessing the likely contributors to violent behavior
already demonstrated by an individual. As my study directly suggests,
individuals who engage in recurrent, extreme violence cannot be
distinguished based on the parental structure of their childhood home. Any
tendency to be reductionist in attributing responsibility to a single-parent
upbringing for frequent, prolonged, and extreme long-term violence is
misguided.
Conclusion
Previous researchers have studied the role of a single-parent
upbringing to negative short- and long-term psychological and behavioral
outcomes, finding a link to violent behavior (Fergusson et al., 2007;
Theobald et al., 2013). To this point, there has been no known research on
the association of a single-parent upbringing with scale of violence. This was
the first study to examine the potential correlation between a singleparent
upbringing and scale of violence as measured by number of suspected
victims, number of confessed victims, number of victims convicted of
killing, and duration of killing among male serial killers who acted alone in
the United States. Male serial killers with a single-parent upbringing were
compared to male serial killers raised by two birth parents across the four
measures of violence scale. The results yielded no significant correlation
between the parental structure of the childhood home and scale of violence.
The study added to the research in the areas of single-parent
upbringing and longterm extreme, recurrent, and prolonged violence.
Limitations and methodological weaknesses of the study support the need
for caution in generalizing the findings. Nonetheless, the results add to
understanding of the relationship between a single-parent upbringing and
violence scale, imposing a limit on the relationship between single-parent
upbringing and violence so as not to include large-scale violence as defined
through frequency and duration. By revealing the limits of the association
between a single-parent upbringing and long-term violence, efforts to predict
long-term violence can focus more precisely on the underlying ACEs that
are frequently, but not exclusively, commensurate with a single-parent
upbringing. The study provides a foundation for additional research of the
ACEs that comprise the single-parent and two birth parent households
studied to identify root factors that may more strongly predict large-scale
violence. Additional recommendations for future study include increasing
the sample size, extending the sample to additional categories of parental
structure in the childhood home, and exploring other groups of serial killers,
such as women, those who operate with a partner or in a group, and those
outside the United States.
