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AssociationofSuicidalBehavior.pdf
RESEARCH ARTICLE
Association of suicidal behavior with exposure
to suicide and suicide attempt: A systematic
review and multilevel meta-analysis
Nicole T. M. HillID 1,2*, Jo RobinsonID
1 , Jane Pirkis
3 , Karl AndriessenID
3 ,
Karolina KrysinskaID 1 , Amber PayneID
1,4 , Alexandra Boland
1 , Alison ClarkeID
1 ,
Allison Milner 5†
, Katrina Witt 1 , Stephan KrohnID
6,7‡ , Amit LampitID
6,7,8‡*
1 Orygen, Centre for Youth Mental Health, University of Melbourne, Parkville, Victoria, Australia, 2 Telethon
Kids Institute, Perth, Western Australia, Australia, 3 Centre for Mental Health, Melbourne School of
Population and Global Health, University of Melbourne, Parkville, Victoria, Australia, 4 Northeastern
University, Boston, Massachusetts, United States of America, 5 Centre for Health Equity, School of
Population and Global Health, University of Melbourne, Parkville, Victoria, Australia, 6 Department of
Neurology, Charité–Universitätsmedizin Berlin, Berlin, Germany, 7 Berlin School of Mind and Brain,
Humboldt-Universität zu Berlin, Berlin, Germany, 8 Department of Psychiatry, University of Melbourne,
Parkville, Victoria, Australia
† Deceased.
‡ These authors are joint senior authors on this work.
* [email protected] (NTMH); [email protected] (AL)
Abstract
Background
Exposure to suicidal behavior may be associated with increased risk of suicide, suicide
attempt, and suicidal ideation and is a significant public health problem. However, evidence
to date has not reliably distinguished between exposure to suicide versus suicide attempt,
nor whether the risk differs across suicide-related outcomes, which have markedly different
public health implications. Our aim therefore was to quantitatively assess the independent
risk associated with exposure to suicide and suicide attempt on suicide, suicide attempt,
and suicidal ideation outcomes and to identify moderators of this risk using multilevel meta-
analysis.
Methods and findings
We systematically searched MEDLINE, Embase, PsycINFO, CINAHL, ASSIA, Sociological
Abstracts, IBSS, and Social Services Abstracts from inception to 19 November 2019. Eligi-
ble studies included comparative data on prior exposure to suicide, suicide attempt, or sui-
cidal behavior (composite measure—suicide or suicide attempt) and the outcomes of
suicide, suicide attempt, and suicidal ideation in relatives, friends, and acquaintances.
Dichotomous events or odds ratios (ORs) of suicide, suicide attempt, and suicidal ideation
were analyzed using multilevel meta-analyses to accommodate the non-independence of
effect sizes. We assessed study quality using the National Heart, Lung, and Blood Institute
quality assessment tool for observational studies. Thirty-four independent studies that pre-
sented 71 effect sizes (exposure to suicide: k = 42, from 22 independent studies; exposure
PLOS MEDICINE
PLOS Medicine | https://doi.org/10.1371/journal.pmed.1003074 March 31, 2020 1 / 27
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OPEN ACCESS
Citation: Hill NTM, Robinson J, Pirkis J,
Andriessen K, Krysinska K, Payne A, et al. (2020)
Association of suicidal behavior with exposure to
suicide and suicide attempt: A systematic review
and multilevel meta-analysis. PLoS Med 17(3):
e1003074. https://doi.org/10.1371/journal.
pmed.1003074
Academic Editor: Vikram Patel, Harvard Medical
School, UNITED STATES
Received: August 12, 2019
Accepted: February 21, 2020
Published: March 31, 2020
Peer Review History: PLOS recognizes the
benefits of transparency in the peer review
process; therefore, we enable the publication of
all of the content of peer review and author
responses alongside final, published articles. The
editorial history of this article is available here:
https://doi.org/10.1371/journal.pmed.1003074
Copyright: © 2020 Hill et al. This is an open access article distributed under the terms of the Creative
Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in
any medium, provided the original author and
source are credited.
Data Availability Statement: All relevant data are
within the manuscript and its Supporting
to suicide attempt: k = 19, from 13 independent studies; exposure to suicidal behavior (com-
posite): k = 10, from 5 independent studies) encompassing 13,923,029 individuals were eli-
gible. Exposure to suicide was associated with increased odds of suicide (11 studies, N =
13,464,582; OR = 3.23, 95% CI = 2.32 to 4.51, P < 0.001) and suicide attempt (10 studies, N = 121,836; OR = 2.91, 95% CI = 2.01 to 4.23, P < 0.001). However, no evidence of an association was observed for suicidal ideation outcomes (2 studies, N = 43,354; OR = 1.85,
95% CI = 0.97 to 3.51, P = 0.06). Exposure to suicide attempt was associated with increased
odds of suicide attempt (10 studies, N = 341,793; OR = 3.53, 95% CI = 2.63 to 4.73, P < 0.001), but not suicide death (3 studies, N = 723; OR = 1.64, 95% CI = 0.90 to 2.98, P =
0.11). By contrast, exposure to suicidal behavior (composite) was associated with increased
odds of suicide (4 studies, N = 1,479; OR = 3.83, 95% CI = 2.38 to 6.17, P < 0.001) but not suicide attempt (1 study, N = 666; OR = 1.10, 95% CI = 0.69 to 1.76, P = 0.90), a finding that
was inconsistent with the separate analyses of exposure to suicide and suicide attempt. Key
limitations of this study include fair study quality and the possibility of unmeasured confound-
ers influencing the findings. The review has been prospectively registered with PROSPERO
(CRD42018104629).
Conclusions
The findings of this systematic review and meta-analysis indicate that prior exposure to sui-
cide and prior exposure to suicide attempt in the general population are associated with
increased odds of subsequent suicidal behavior, but these exposures do not incur uniform
risk across the full range of suicide-related outcomes. Therefore, future studies should
refrain from combining these exposures into single composite measures of exposure to sui-
cidal behavior. Finally, future studies should consider designing interventions that target sui-
cide-related outcomes in those exposed to suicide and that include efforts to mitigate the
adverse effects of exposure to suicide attempt on subsequent suicide attempt outcomes.
Author summary
Why was this study done?
• Exposure to suicidal behavior in others has been linked to increased risk of suicidal
behavior, but it is not known whether the association differs between types of exposure
(suicide versus suicide attempt) or different outcome measures of suicidal thoughts and
behaviors.
• Distinguishing the relationships of different exposure types with outcomes is important
for the development of targeted interventions and public health approaches to suicide
prevention.
What did the researchers do and find?
• We conducted a systematic review and meta-analysis of 34 studies that investigated the
independent associations between exposure to different types of suicidal behavior and
subsequent suicide, suicide attempt, and suicidal ideation outcomes.
PLOS MEDICINE Association of suicidal behavior with exposure to suicide and suicide attempt: A multilevel meta-analysis
PLOS Medicine | https://doi.org/10.1371/journal.pmed.1003074 March 31, 2020 2 / 27
Information files. Summary data used in the
analyses are provided as S1 Data.
Funding: NH is a PhD student and was supported
by the Australian Rotary Health PhD Partnership
Scholarship (https://australianrotaryhealth.org.au).
JR was supported by a National Health and Medical
Research Council (NHMRC) Career Development
Fellowship (APP1142348, https://www.nhmrc.gov.
au). KA was supported by a NHMRC Early Career
Fellowship (APP1157796, https://www.nhmrc.gov.
au). AM was supported by a Victorian Health and
Medical Research Fellowship, Department of
Health and Human Services (https://www.vic.gov.
au). KW was supported by a post-doctoral
fellowship awarded by the American Foundation for
Suicide Prevention (PDF-0-145-16, https://afsp.
org). SK was supported by the German Federal
Ministry for Education and Research (BMBF grant
13GW0206D, https://www.bmbf.de). AL was
supported by a NHMRC-Australian Research
Council Dementia Research Development
Fellowship (APP1108520, https://www.nhmrc.gov.
au). The funders had no role in study design, data
collection and analysis, decision to publish, or
preparation of the manuscript.
Competing interests: The authors have declared
that no competing interests exist.
Abbreviations: OR, odds ratio.
• We showed that exposure to suicide is associated with increased odds of both suicide
and suicide attempt, but found limited evidence of an association with suicidal ideation.
Exposure to suicide attempt was associated with increased odds of suicide attempt only.
• For exposure to suicide, degree of relationship (i.e., whether the suicide exposure
occurred in a relative as compared to a friend or acquaintance) did not materially affect
the magnitude of the association. The odds of suicidal behavior (i.e., including
attempted suicide) were, however, greater when the exposure occurred in a relative.
What do these findings mean?
• Exposure to suicide is associated with greater odds of suicide and suicide attempt. Yet,
exposure to suicide attempt is associated with increased odds of suicide attempt only.
• Researchers and public health practitioners should refrain from combining suicide, sui-
cide attempt, and suicidal ideation into composite measures of suicide exposures and
outcomes.
• We recommend that future public health policy include the potential adverse effects of
exposure to suicide attempt.
Introduction
Suicide attempt and suicide are leading causes of global morbidity and mortality. Approxi-
mately 800,000 people die by suicide annually [1], of which about one-third are under the age
of 30 [2]. The prevalence of suicide attempt is significantly greater than that of suicide death
and is associated with heightened risk of later death by suicide [3,4] as well as psychosocial
adversities that persist later in life [5]. For every suicide death, it is estimated that approxi-
mately 135 people are affected [6]. Over the course of a lifetime, the proportion of people
exposed to the suicide of a relative, friend, or acquaintance is approximately 21% [7]. Exposure
to suicide has been linked to increased risk of physical disease and adverse mental health
including depression, posttraumatic stress disorder, and complicated grief [8,9]. The deleteri-
ous effects associated with exposure to suicide may also render some people, particularly ado-
lescents and young adults, at increased risk of suicide and suicide attempt [10].
Combined, the large number of people exposed to suicide and the potential increased risk
of suicide-related outcomes (suicide, suicide attempt, and suicidal ideation) in others mean
that exposure to suicide is a significant public health concern [1]. This is reflected in several
national suicide prevention strategies that recommend postvention interventions for those
bereaved by suicide [11], as well as several international frameworks for the prevention of sui-
cide-related contagion, and the management of suicide and self-harm clusters [12–15]. These
public health strategies have largely focused on exposure to suicide, despite a growing body of
evidence that suggests that exposure to suicide attempt, the behavior most proximal to suicide,
may also be associated with increased risk of suicide-related outcomes [16–19].
Distinguishing between the potential independent effects of exposure to suicide and suicide
attempt is important since measures of morbidity and mortality have markedly different pub-
lic health implications. Yet evidence regarding the independent effects of exposure to suicide
and suicide attempt on subsequent suicide-related outcomes is unclear. A systematic review
PLOS MEDICINE Association of suicidal behavior with exposure to suicide and suicide attempt: A multilevel meta-analysis
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and meta-analyses by Geulayov and colleagues [20] showed that exposure to suicide and expo-
sure to suicide attempt of a parent were associated with increased risk of suicide and suicide
attempt in offspring. However, the authors pooled mean effect sizes across subgroups within
studies and did not take into account the dependencies between effect sizes, an approach that
may distort the results of the meta-analyses [21]. Another systematic review by Crepeau-Hob-
son and Leech [19] reported that both exposure to suicide and exposure to suicide attempt
were associated with subsequent suicide-related behavior among friends or acquaintances. But
the authors did not adequately control for studies that reported lifetime prevalence, leaving the
causal direction between exposure to suicide attempt and subsequent suicide-related outcomes
unclear.
Lack of guiding evidence has impeded translation of the evidence into practice. For exam-
ple, it is not currently clear which populations may be at risk, nor whether the risk differs
across outcomes involving suicide, suicide attempt, and suicidal ideation. Sveen and Walby
[22] found inconclusive evidence supporting a relationship between exposure to suicide and
increased risk of suicide-related behavior in others. However, the authors combined studies
reporting exposure in relatives and friends or acquaintances, which may incur different suicide
risk. More recently, systematic reviews that investigated exposure to suicide in friends and
acquaintances have reported a positive association between exposure to suicide and subse-
quent suicide-related outcomes [19,23]. Yet, as noted previously, the causal direction between
exposure and outcome measures were confounded by the inclusion of studies that reported
lifetime prevalence of exposure and outcome measures. Lastly, some studies included outcome
measures that combined suicidal ideation with suicide attempt [24,25] or combined exposure
to suicide and exposure to suicide attempt as a composite measure of exposure to suicidal
behavior [26–28]. Composite measures of exposure to suicidal behavior prevent us from iden-
tifying whether the observed effect is influenced by a true association or the result of a cumula-
tive effect.
Consequently, the effects of prior exposure to suicide and suicide attempt on suicide-related
outcomes have not been reliably quantified, and the factors that moderate this risk are not cur-
rently known. We therefore aimed to conduct a systematic review and multilevel meta-analysis
investigating the independent association between prior exposure to suicide, suicide attempt,
and suicidal behavior (composite measure—suicide or suicide attempt) and subsequent sui-
cide, suicide attempt, and suicidal ideation in relatives, friends, and acquaintances. In doing
so, we aimed to quantify the association between exposure to suicide and suicide attempt and
the full range of suicide-related outcomes, and to identify whether factors such as relationship
to the person who engaged in the initial suicidal act, age of the study population, and study
design characteristics moderate this risk. By using multilevel meta-analyses, we were able to
account for dependencies among multiple effect sizes taken from the same cohort within a
study, an extremely common and challenging aspect of conducting meta-analyses of epidemi-
ological studies [29].
Methods
This work adheres to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-
Analyses) [30] and MOOSE (Meta-analysis of Observational Studies in Epidemiology) [31]
guidelines (S1 Text) and was prospectively registered with PROSPERO (CRD42018104629).
Deviations from the protocol include the use of exposure to suicidal behavior (composite) and
statistical analyses using multilevel meta-analyses. The association between exposure to suicide
and suicide attempt and grief and mental health outcomes will be reported in a separate sys-
tematic review and meta-analysis.
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Electronic search strategy
We searched MEDLINE, Embase, PsycINFO, Cumulative Index to Nursing and Allied Health
Literature (CINAHL), Applied Social Sciences Index and Abstracts (ASSIA), Sociological
Abstracts, International Bibliography of the Social Sciences (IBSS), and Social Services
Abstracts from inception through 19 November 2019 for observational studies examining the
effects of exposure to suicide, suicide attempt, or suicidal behavior on 1 or more outcomes
relating to suicide, suicide attempt, or suicidal ideation. Search terms relating to exposure to
suicide and suicide attempt as well suicide bereavement, suicide contagion, and suicide clus-
ters were combined using Boolean logic (S2 Text). The search was not limited by time, loca-
tion, year of publication, or language (articles written in a language other than English were
translated using Google Translate). Additional articles were identified by scanning the refer-
ence lists of included articles and previous reviews. One author (NTMH) conducted the initial
search and screening of titles and abstracts. Three authors independently screened the full text
of each potentially eligible article (NTMH, AB, KA, and KW). Discrepancies were resolved by
the first author (NTMH), who also contacted the corresponding authors of primary studies for
additional information.
Study selection and eligibility criteria
Eligible studies reported dichotomous events (both the exposure and outcome were reported
as having occurred or not occurred, yielding a 2 × 2 matrix) or odds ratios (ORs) for exposure to suicide, suicide attempt, or suicidal behavior and subsequent suicide, suicide attempt, or
suicidal ideation. Exposure to suicide, suicide attempt, or suicidal behavior was determined
from self-reported measures, informant interviews, official records (such as hospital admission
records), or data linkage to death certificates. Outcomes involving suicide, suicide attempt, or
suicidal ideation were determined from self-reported measures, informant interviews, or offi-
cial records, such as death certificates, coroner reports, or hospital admission records. Cohort,
case–control, and cross-sectional study designs were eligible if the study was reported in a
peer-reviewed journal and the temporal sequence between the exposure and outcome was
specified. For cross-sectional studies, the temporal sequence between exposure and outcome
was established if the outcome measurement occurred after the exposure (e.g., the study asked
participants if they had made a suicide attempt after exposure to the suicide of another). Par-
ticipants of any age who were exposed to prior suicide or suicide attempt were eligible if the
sample was mainly, or solely, drawn from the general population, as opposed to a clinical or
other high-risk population (e.g., inpatients or prison detainees). Eligible control groups
included individuals who did not report prior exposure to suicide, suicide attempt, or suicidal
behavior in others.
Studies were excluded if findings from a non-exposed (control) group were not reported,
or the control group was composed of participants exposed to other modes of death (e.g., acci-
dent or natural causes). Studies that reported estimates of lifetime prevalence as well as studies
that did not establish the temporal sequence between exposure and suicide-related outcomes
(e.g., the study reported 12-month prevalence of the outcome, but prior exposure to suicide
was not indicated) were excluded. Finally, studies that reported outcomes following exposure
to media reports of suicide (including fictional and non-fictional portrayals) or non-suicidal
self-injury were excluded.
Data collection and coding
Two independent reviewers (NTMH and KK) extracted data using a standardized data collec-
tion form. A description of the a priori moderators of risk included in the study are presented
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in S1 Table. Dichotomous data were favored over ORs. When dichotomous events were not
available, unadjusted ORs were recorded. For studies with multiple follow-up time points,
only data from the longest time point were extracted [32]. Studies that included participants
from the same population during overlapping time periods (e.g., nationwide data registry stud-
ies that reported suicide deaths from overlapping time periods) were included only if the stud-
ies reported different relationships (e.g., relatives and friends and acquaintances) or different
suicide-related outcomes. When studies combined measures of exposure to the suicide of a rel-
ative or friend, we contacted primary authors for disaggregated data. If these data were not
available, the relationship between the exposed individual and the individual(s) who engaged
in suicidal behavior was determined by a majority rule (the relationship that occurred most
frequently as indicated in >50% of the total sample). Similarly, if the age of participants
included a combination of youths and adults, the age of the population was categorized in
favor of the age group that exceeded 50% of the overall population. Study-level data are pro-
vided as S1 Data.
Multilevel meta-analysis rationale and data analysis
Since 16/34 (47%) studies reported multiple exposure and/or outcome measures in the same
sample of participants, the assumption of independent estimates for a traditional meta-analysis
was not met. We therefore used a 3-level meta-analysis, which parallels traditional random
effects meta-analyses. The main difference is that dependent effect sizes (due to multiple sub-
groups or outcome measures within studies) are nested within studies (level 2) before these are
pooled across studies (level 3). Thus, t2 ð2Þ
is the variance within studies while t2 ð3Þ
is the variance
between studies. This approach allows for the investigation of heterogeneity not only between
but also within studies [33]. For clarity, we use the general term “multilevel” throughout to
describe our analyses.
We conducted a multilevel meta-analysis with the maximum likelihood estimation method
using the metaSEM package [34] for R version 3.6.0. For the main analysis, we used dichoto-
mous event data to calculate the pooled OR with the accompanying 95% confidence interval
(CI) for risk of suicide, suicide attempt, and suicidal ideation within exposed and non-exposed
individuals. When event data were not available, we used unadjusted ORs. Meta-analyses were
conducted separately for exposure to suicide, suicide attempt, and suicidal behavior. Heteroge-
neity was quantified as variance in true effects within (t2 ð2Þ
) and between (t2 ð3Þ
) studies. We also
report the I2 statistic, which represents the proportion of variance in true effects out of total variance for each level (i.e., I2
ð2Þ and I2
ð3Þ ), along with its 95% confidence interval. Maximum
likelihood mixed-effects analyses were used to examine effect moderators via subgroup analy-
sis and to explain heterogeneity (quantified as R2) for each level. Since the multilevel model does not provide study-level effect estimates, forest plots present the mean OR of each study
but report the pooled 3-level estimate. Small study effect (“publication bias”) was assessed by
visually inspecting funnel plots of mean log ORs against standard error for asymmetry [35].
When at least 10 studies were available for analysis, we formally assessed funnel plot asymme-
try using a multilevel analogue of Egger’s test of the intercepts [36].
Risk of bias and quality assessment
Study quality was assessed using the National Heart, Lung, and Blood Institute quality assess-
ment tool for observational studies [37]. The original tool contains 14 criteria that determine
potential sources of bias in the study population and selection of participants, outcome and
exposure measurement, blinding, confounding, and attrition. An overall rating of “good,”
PLOS MEDICINE Association of suicidal behavior with exposure to suicide and suicide attempt: A multilevel meta-analysis
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“fair,” or “poor” was provided for each independent study. Three independent reviewers con-
ducted assessments (NTMH, AP, and AC), and any discrepancies were settled through discus-
sion and finalized by the primary author (NTMH).
Results
Study selection
The initial search identified 21,868 records, of which 8,320 were duplicates. A total of 13,548
records were screened based on title and abstract (Fig 1). The full-text versions of 760 records
were assessed, 10 of which were obtained from searching the reference lists of existing reviews.
The authors of 6 studies were contacted [38–43], and information or additional data provided
for 2 studies [39,41]. A total of 167 records reported outcomes relating to suicide, suicide
attempt, or suicidal ideation. Of these, 73 articles reported lifetime prevalence estimates, 35
studies involved overlapping populations or superseded time points, and 2 studies did not
report ORs or accompanying effect sizes: These articles were therefore excluded from the meta-
analysis. One study [44] was excluded because it reported an OR of 36.4, and 1 study [45] was
excluded because it reported an OR of 18; both studies were prone to artifacts introduced by
quasi-separation (S2 Table; S3 Text). The final dataset included 34 independent studies, which
comprised 71 effect sizes (exposure to suicide: k = 42 across n = 22 studies; exposure to suicide attempt: k = 19 across n = 13 studies; exposure to suicidal behavior: k = 10 across n = 5 studies).
Characteristics of studies
Thirty-four studies were included in the meta-analysis (N = 13,923,029; Table 1). In terms of exposure to suicide, 22 studies (N = 13,607,708) provided a total of 42 effect sizes for suicide (k = 24), suicide attempt (k = 15), and suicidal ideation (k = 3). For exposure to suicide attempt, 13 studies (N = 342,516) provided a total of 19 effect sizes for suicide (k = 3) and suicide attempt (k = 16). For exposure to suicidal behavior (composite measure—suicide or suicide attempt), 5 studies (N = 2,145) provided a total of 10 effect sizes for suicide (k = 7) and suicide attempt (k = 3). Studies were from a range of geographic settings including Australia/New Zea- land [46–48], North America [16,18,28,49–57], Europe [17,41,58–63], East Asia [26,27,64–69],
the Middle East [39,42], and South America [70]. Overall, 20/34 studies involved youths aged
25 years or less. Overall exposure was determined by informant interviews in 14/34 (41%)
studies, self-report measures in 12/34 (35%) studies, and official death records in 8/34 (24%)
studies. A total of 6/34 (18%) studies reported separate effect sizes for exposure to suicide and
exposure to suicide attempt, and 5/34 (15%) studies reported effect sizes for both exposure in
relatives and exposure in friends. In terms of outcome measurements, most studies (23/34,
68%) used official hospital admission or death records, followed by self-report measures (10/
34, 29%) and informant interviews (1/34, 3%). One study (1/34, 3%) reported outcomes for
both suicide attempt and suicidal ideation following exposure to suicide. No studies reported
suicidal ideation outcomes following exposure to suicide attempt or suicidal behavior. Lastly, 3
studies included exposure and outcome measurements of deliberate self-harm, irrespective of
intent [48,59,62]. The remaining studies did not define suicide attempt [16,18,42,52,54,57,
59,70], or defined suicide attempt as an act involving explicit intent to die [16,17,28,39,47,49–
51,53,56,64].
Study quality
Studies were most commonly rated fair (13/34) and good (13/34), followed by poor (8/34; S3
Table). The 13 good-quality studies tended to comprise cohort or case–control study designs
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and had clearly defined and valid exposure and outcome measures that were verified using
official hospital or death records. The 8 studies that were rated poor tended to combine
Fig 1. Flowchart of included studies.
https://doi.org/10.1371/journal.pmed.1003074.g001
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Table 1. Characteristics of included studies.
Study, location,
study design
Exposed
population, mean
age or age range
(years), percent
female, total sample
size
Exposure Definition of exposure Outcome(s) Definition of outcome(s) Exposure ascertainment Study
quality
Agerbo 2003 [58],
Denmark, case–
control
Adult b , age
range = 9–44,
24.52% female, N = 4,444,297
Suicide of relative (any
relative) a
Official records: Cause of
death register. Exposure(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959),
intentional self-harm (ICD-
10: X60–X84), and sequelae
of intentional self-harm
(ICD-10: Y870).
Suicide Official death records: Cause
of death register. Outcome(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959),
intentional self-harm (ICD-
10: X60–X84), and sequelae
of intentional self-harm
(ICD-10: Y870).
The outcome occurred after
the date of the exposure
determined through data
linkage.
Good
Almeida 2012 [46],
Australia, cross-
sectional
Adult, mean
age = 70.5, age
range = 60–101,
58.7% female, N = 21,290
Suicide of relative (first-
degree relative) b
Self-report: Participants were
asked if any immediate family
member had died by suicide.
Suicidal
ideation
Self-report: Participants
completed the Depressive
Symptom Inventory
Suicidality Subscale.
Determined by current
suicidal ideation (persistent
over the last 2 weeks).
Exposure occurred at least 2
months prior.
Good
Brent 1996a [51],
US, cohort
Youth, mean
age = 20.8, 46.6%
female, N = 341
Suicide of friend or
acquaintance
Informant: Suicide death in
the family.
Suicide
attempt
Self-report: Participants were
asked if they have engaged in
deliberate self-harm with
intent to die.
New onset of suicide
attempt since exposure.
Good
Brent 1996b [50],
US, cohort
Youth, mean
age = 20.2, 50%
female, N = 44
Suicide of relative
(sibling)
Self-report: Suicide death in
the family.
Suicide
attempt
Self-report: Participants were
asked if they have engaged in
deliberate self-harm with
intent to die.
New onset of suicide
attempt since exposure.
Good
Christiansen 2011
[59], Denmark,
case–control
Youth, mean
age = 17.49, 78.75%
female, N = 69,649
Suicide of relative
(parent)
Official records: Exposure(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959)
and intentional self-harm
(ICD-10: X60–X84).
Suicide
attempt
Hospital admission records:
Outcome(s) determined by
ICD codes for suicide and
self-inflicted injury (ICD-8/9:
E950–E959), intentional self-
harm (ICD-10: X60–X84),
self-poisoning event of
undetermined intent (ICD-
10: Y10–Y34), injury of
muscle and tendon at neck
level (ICD-10: S617–S619),
sequelae of poisoning by
drugs, medicaments and
biological substances (ICD-
10: T36–T60), and toxic effect
of unspecified substance
(ICD-10: T65).
The outcome occurred after
the date of the exposure
determined through data
linkage.
Good
Gravseth 2010 [61],
Norway, cohort
Adult b , age
range = 19–37,
48.82% female, N = 610,359
Suicide of relative
(parent)
Official records: Exposure(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959)
and intentional self-harm
ICD-10: (X60–X84).
Suicide Official death records:
Outcome(s) determined by
ICD codes for suicide and
self-inflicted injury (ICD-9:
E950–E959) and intentional
self-harm (ICD-10: X60–
X84).
The outcome occurred after
the date of the exposure
determined through data
linkage.
Good
Giupponi 2018 [41],
Italy, case–control a
Adult, mean
age = 48.25, 38.16%
female, N = 262
Suicide of relative (any
relative)
Informant: Participants were
asked if there was a history of
suicide in the family.
Informed by at least 2 people
including relatives or close
friends.
Suicide Official death records: Cause
of death hospital forensic
post-mortem records.
Psychological autopsy—
suicide occurred after
exposure.
Fair
Lee 2018 [66],
Taiwan, cohort
Youth, 63.4% aged
<17, 47.75% female,
N = 438,330
Suicide of relative
(parent)
Official records: Taiwan
death registry. Exposure(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959),
intentional self-harm (ICD-
10: X60–X84), and sequelae
of intentional self-harm
(ICD-10: Y870).
Suicide Official death records:
Taiwan death registry.
Outcome(s) determined by
ICD codes for suicide and
self-inflicted injury (ICD-8/9:
E950–E959), intentional self-
harm (ICD-10: X60–X84),
and sequelae of intentional
self-harm (ICD-10: Y870).
The outcome occurred after
the date of the exposure
determined through data
linkage.
Good
(Continued)
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Table 1. (Continued )
Study, location,
study design
Exposed
population, mean
age or age range
(years), percent
female, total sample
size
Exposure Definition of exposure Outcome(s) Definition of outcome(s) Exposure ascertainment Study
quality
Liu 2019 [67],
China, case–
control a
Adult, mean
age = 60.87, 43.15%
female, N = 380
Suicide of relative (any
relative)
Informant: Informants were
asked if there was a history of
suicide in the family.
Informed by at least 1 relative
or close friend.
Suicide Official death records: Center
for Disease Control and
Prevention records of suicide.
Psychological autopsy—
suicide occurred after
exposure.
Fair
Conner 2007 [64],
China, case–control
Adult b , age range
<18 to 55+ (64%
aged <35), 76%
female, N = 554
Suicide of friend or
acquaintance c
Self-report: Participants were
asked if there was a history of
suicide in an associate or
relative.
Suicide
attempt
Hospital admission records:
Hospital admission for
intentional suicide attempt.
All participants were
hospitalized for suicide
attempt at the time that
prior exposure was
measured.
Fair
Foster 1999 [60],
Ireland, case–
control a
Adult b , age range
<20 to 79 (32%
aged <29), 28.2%
female, N = 230
Suicide of relative (any
relative)
Informant: Informants were
asked if there was a family
history of suicide. Informants
not indicated but were
“bereaved” by suicide.
Suicide Official death records:
Coroner-determined suicide
death.
Psychological autopsy—
suicide occurred after
exposure.
Fair
Gray 2014 [55], US,
case–control a
Adult, mean
age = 39.9, 32.5%
female, N = 423
Suicide of relative (any
relative)
Informant: Informants were
asked if there was a family
history of suicide. Informed
by next of kin.
Suicide Official death records: Cause
of death register, Utah Office
of the Medical Examiner.
Psychological autopsy—
suicide occurred after
exposure.
Fair
Katibeh 2018 [42],
Iran, case–control
Youth, mean
age = 15.5, age
range � 18, percent
female not reported,
N = 300
Suicide of relative
(parent)
Self-report: Participants were
asked if there was a history of
suicide in their parents.
Suicide
attempt
Hospital admission records:
Hospital admission records
for suicide attempt.
All participants were
hospitalized for suicide
attempt at the time that
prior exposure was
measured.
Poor
Swanson & Colman
2013 [57], Canada,
cohort (cross-
sectional analyses)
Youth, age
range = 12–15,
50.1% female, N = 22,064
Suicide of friend or
acquaintance
Self-report: Participants were
asked whether anyone in
their school had died by
suicide (schoolmate’s suicide)
and whether they personally
knew anyone who had died
by suicide.
Suicide
attempt
and suicidal
ideation
Self-report (suicide attempt):
Participants were asked to
report the number of suicide
attempts they had made in
the past year, and participants
were asked if they had
seriously considered
attempting suicide in the past
year.
Prior exposure measured at
baseline, and subsequent
suicide attempt was based
on participants who
reported having made a
suicide attempt within the
2-year follow-up period.
Fair
Tidemalm 2011
[63], Sweden, case–
control
Adult b , population-
based study (all
ages), age/sex not
reported, N = 7,969,645
Suicide of relative
(sibling, parent, or
spouse)
Official records: Cause of
death register. Exposure(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959),
intentional self-harm (ICD-
10: X60–X84), and sequelae
of intentional self-harm
(ICD-10: Y870).
Suicide Official death records: Cause
of death register. Outcome(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959),
intentional self-harm (ICD-
10: X60–X84), and sequelae
of intentional self-harm
(ICD-10: Y870).
The outcome occurred after
the date of the exposure.
Good
Vijayakumar 1999
[69], India, case–
control a
Adult b , age
range = 15 to 60+
(48.5% aged �24),
45.0% female, N = 200
Suicide relative (any
relative)
Informant: Informants were
asked if there was a history of
completed suicide in the
family. Informed by family
members.
Suicide Official death records:
Coroner-determined suicide
death.
Psychological autopsy—
suicide occurred after
exposure.
Fair
Brent 2015 [49], US,
cohort
Youth, mean
age = 17.7, 48.1%
female, N = 42
Suicide attempt of
relative (parent)
Informant: Informants were
asked if a family member had
made a suicide attempt,
defined as a self-destructive
act that resulted in potential
or actual tissue damage with
inferred or explicit intent to
die. Informed by parents of
cases and controls.
Suicide
attempt
Self-report: Participants were
asked if they had made a
suicide attempt, defined as a
self-destructive act that
resulted in potential or actual
tissue damage with inferred
or explicit intent to die.
Number of new events of
suicide attempt during
5-year follow-up period.
Good
(Continued)
PLOS MEDICINE Association of suicidal behavior with exposure to suicide and suicide attempt: A multilevel meta-analysis
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Table 1. (Continued )
Study, location,
study design
Exposed
population, mean
age or age range
(years), percent
female, total sample
size
Exposure Definition of exposure Outcome(s) Definition of outcome(s) Exposure ascertainment Study
quality
Gould 1996 [54],
US, case–control a
Youth, age
range � 18, 20.1%
female, N = 267
Suicide attempt of
relative (parent)
Informant: Informants were
asked if there was a history of
first- and second-degree
relatives who died by suicide
or made a suicide attempt.
Informed by parents or other
adult who lived with the
deceased.
Suicide Official death records:
Coroner-determined suicide
death.
Psychological autopsy—
suicide occurred after
exposure.
Fair
Hu 2017 [48],
Australia, case–
control
Youth, age
range = 10–19,
62.4% female, N = 150,171
Suicide attempt of
relative (parent)
Official records: Data linkage
records for admission to
hospital for deliberate self-
harm.
Suicide
attempt
Hospital admission records:
Outcome(s) determined by
ICD codes for suicide and
self-inflicted injury (ICD-8/9:
E950–E959), injury
undetermined whether
accidentally or purposely
inflicted (ICD-8/9: E980–
E989), intentional self-harm
(ICD-10: X60–X84), and
sequelae of intentional self-
harm (ICD-10: Y870).
The outcome occurred after
the date of the exposure
determined through data
linkage.
Good
Lewinsohn 1994
[56], US, cohort
Youth, mean
age = 16.5, age
range = 14–18, 54%
female, N = 1,508
Suicide attempt of
friend or acquaintance
Self-report: Participants were
asked if they knew a friend
who had attempted suicide.
Suicide
attempt
Self-report: Participants were
asked if they have made an
attempt to kill themselves.
Prior exposure measured at
baseline, and subsequent
suicide attempt was based
on participants who
reported having made a
suicide attempt within the
1-year follow-up period.
Good
Mittendorfer-Rutz
2008 [62], Sweden,
case–control
Youth, mean
age = 19.1, 66.9%
female, N = 158,840
Suicide attempt of
relative (first-degree
relative)
Official records: Hospital
admissions inpatient care
register. Exposure(s)
determined by ICD codes for
suicide and self-inflicted
injury (ICD-8/9: E950–E959),
injury undetermined whether
accidentally or purposely
inflicted (ICD-8/9: E980–
E989), intentional self-harm
(ICD-10: X60–X84), and
sequelae of intentional self-
harm (ICD-10: Y870).
Suicide
attempt
Hospital admission records:
Outcome(s) determined by
ICD codes for suicide and
self-inflicted injury (ICD-8/9:
E950–E959), injury
undetermined whether
accidentally or purposely
inflicted (ICD-8/9: E980–
E989), intentional self-harm
(ICD-10: X60–X84), and
sequelae of intentional self-
harm (ICD-10: Y870).
All participants were
hospitalized for deliberate
self-harm at the time that
prior exposure was
measured.
Good
Nrugham 2008 [17],
Norway, cohort
Youth, mean
age = 14.9, age
range = 15–20,
50.8% female, N = 265
Suicide attempt of
friend or acquaintance
Self-report: Participants were
asked if they knew a friend
who had attempted suicide.
Suicide
attempt
Self-report: Participants were
asked if they have ever tried
to intentionally commit
suicide.
Prior exposure measured at
baseline, and subsequent
suicide attempt was based
on participants who
reported having made a
suicide attempt within the
1-year follow-up period.
Poor
Hishinuma 2018
[16], US, cohort
Youth, age
range = 13–21, 54%
female, N = 2,083
Suicide attempt of
relative (any relative)
and suicide attempt of
friend or acquaintance
Self-report: Participants were
asked if a family member or
friend had tried to commit
suicide.
Suicide
attempt
Self-report: Participants were
asked if they had tried to
commit suicide in the past 6
months (Major Life Events
Scale).
Prior exposure measured at
baseline, and subsequent
suicide attempt was based
on participants who
reported having made a
suicide attempt during the
5-year follow-up period.
Good
Ahmadi 2015 [39],
Iran, case–control
Youth, mean
age = 29 (60% aged
�25), 76.0% female,
N = 453
Suicide of relative (first
and second degree) and
suicide attempt of
relative (first and
second degree)
Self-report: Suicide history in
family and sibling, and
parent’s history of suicide
attempt.
Suicide
attempt
Hospital admission records:
Hospital admission for
deliberate self-inflicted
immolation with suicide
intent.
All participants were
hospitalized for suicide
attempt at the time that
prior exposure was
measured.
Fair
(Continued)
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Table 1. (Continued )
Study, location,
study design
Exposed
population, mean
age or age range
(years), percent
female, total sample
size
Exposure Definition of exposure Outcome(s) Definition of outcome(s) Exposure ascertainment Study
quality
Chachamovich 2015
[52], Canada, case–
control a
Youth, mean
age = 23.4 d
age
range = 1–25, 7.5%
female, N = 240
Suicide of relative (any
relative); suicide
attempt of relative (any
relative)
Informant: Informants were
asked if there was a history of
suicide completion or suicide
attempt in family. Informed
by spouses, parents, or close
friends of the deceased.
Suicide Official death records:
Coroner-determined suicide
death.
Psychological autopsy—
suicide occurred after
exposure.
Fair
Chan 2018 [47],
New Zealand, cross-
sectional
Youth, age
range = 13–19
(98.7% aged �17),
54.3% female, N = 8,497
Suicide of relative (any
relative) and friend or
acquaintance; suicide
attempt of relative (any
relative) and friend or
acquaintance
Self-report: Participants were
asked if there was a history of
suicide among their family or
friends. For exposure to
suicide attempt, participants
were asked if anyone in their
family or friends ever tried to
kill themselves (attempted
suicide?).
Suicidal
ideation
Self-report: Participants were
asked if they have made an
attempt to kill themselves.
Exposure occurred >1 year
ago, but ideation based on
symptoms in the past year.
Fair
Garfinkel 1982 [53],
Canada, case–
control
Youth, mean
age = 15.2, age
range = 6–21, 75.4%
female, N = 1,010
Suicide of relative
(parent); suicide
attempt of relative
(parent)
Official records: Chart review
of family history of suicide
attempts or suicide
(completed suicide).
Suicide
attempt
Hospital admission records:
Hospital admission for
suicide attempt with a
conscious intent to die.
All participants were
hospitalized for suicide
attempt at the time that
prior exposure was
measured.
Poor
Palacio 2007 [70],
Colombia, case–
control a
Adult b , median
age = 29, 19.4%
female, N = 216
Suicide of relative (any
relative); suicide
attempt of relative (any
relative)
Informant: Informants were
asked if there was a history of
suicide or suicide attempt in
the family. Informed by
relatives and medical
documents.
Suicide Official death records:
Medical legal records of
suicide cause of death.
Psychological autopsy—
suicide occurred after
exposure.
Poor
Thompson 2011
[18], US, cohort
Youth, mean
age = 15.5, age
range = 11–21,
49.1% female, N = 18,924
Suicide of relative (any
relative) a
and friend or
acquaintance; suicide
attempt of relative (any
relative) a
and friend or
acquaintance
Self-report: Participants were
asked if a friend or family
member had died by suicide.
For exposure to suicide
attempt, participants were
asked if a friend or family
member had made a suicide
attempt.
Suicide
attempt
Self-report: Participants were
asked whether they had
attempted suicide within the
12 months before the survey.
Prior exposure measured at
baseline, and subsequent
suicide attempt was based
on participants who
reported having made a
suicide attempt during wave
III (7 years later).
Fair
Phillips 2002 [68],
China, case–
control a
Adult b , age
range = 10 to 75+
(70% aged �30),
52% female, N = 1,055
Suicidal behavior
(composite) of relative
(any relative)
Informant: Informants were
asked if there was a family
history of suicidal behavior
(suicide attempts or suicide).
Informed by family members
of the deceased or close
associates.
Suicide Official death records:
Medical legal records of
suicide cause of death.
Psychological autopsy—
suicide occurred after
exposure.
Poor
Cheng 2000 [26],
Taiwan, case–
control a
Adult b , mean
age = 43.9, age
range = 15–60,
39.8% female, N = 339
Suicidal behavior
(composite) of relative
(any relative)
Informant: Informants were
asked if there was a family
history of suicidal behavior
(suicide attempts or suicide).
Informed by family members
of the deceased.
Suicide Official death records: Suicide
as determined by prosecutor
and coroner reports.
Psychological autopsy—
suicide occurred after
exposure.
Poor
Maniam 1994 [27],
US, case–control a
Adult b , mean
age = 28.5, age
range = 11–75, 50%
female, N = 40
Suicidal behavior
(composite) of relative
(any relative)
Informant: Informants were
asked if there was a family
history of suicidal behavior
(suicide attempts or suicide).
Informed by parents, spouses,
or other adults who lived with
the deceased.
Suicide Official death records:
Medical legal records of
suicide cause of death.
Psychological autopsy—
suicide occurred after
exposure.
Poor
Jollant 2014 [65],
US, case–control a
Youth, age
range = 15–64
(56.25% aged �24),
25% female, N = 45
Suicidal behavior
(composite) of relative
(any relative)
Informant: Informants were
asked if there was a family
history of suicidal behavior
(suicide attempts or suicide).
Informed by members of the
community who knew the
deceased.
Suicide Informant: Suicide death
reported by informants.
Psychological autopsy—
suicide occurred after
exposure.
Poor
(Continued)
PLOS MEDICINE Association of suicidal behavior with exposure to suicide and suicide attempt: A multilevel meta-analysis
PLOS Medicine | https://doi.org/10.1371/journal.pmed.1003074 March 31, 2020 12 / 27
exposure to suicide and suicide attempt into a composite measure of exposure to suicidal
behavior, did not provide adequate definitions of exposure to suicide or suicide attempt, and
did not provide information on case ascertainment for suicide-related outcomes.
Results of the multilevel meta-analysis
Exposure to suicide. Across 42 effect sizes from 22 studies, exposure to suicide was associated
with 2.94-fold (95% CI = 2.30 to 3.75, P < 0.001; Fig 2) increased odds of suicidal behavior (suicide or suicide attempt). Heterogeneity within and between studies was comparable (t2
ð2Þ =
0.13, I2 ð2Þ
= 47%, 95% CI 15% to 94%; t2 ð3Þ
= 0.132, I2 ð3Þ
= 48%, 95% CI 1% to 81%). The funnel
plot revealed evidence of asymmetry, which may indicate evidence of small study effect
(Egger’s intercept = 0.675, 1-tailed P = 0.06; S1 Fig). Results from the subgroup analysis showed that exposure to suicide was associated with increased odds of suicide (k = 24, OR = 3.23, 95% CI = 2.32 to 4.51, P < 0.001) and suicide attempt (k = 15, OR = 2.91, 95% CI = 2.01 to 4.23, P < 0.001). However, there was no evidence of an association with suicidal ideation (k = 3, OR = 1.85, 95% CI = 0.97 to 3.51, P = 0.06; Q between subgroups = 2.22, df = 2, P = 0.33, R2
ð2Þ = 11.8%, R2
ð3Þ = 0%). The odds of later suicidal behavior were comparable
when the exposure to suicide occurred in relatives (k = 34, OR = 3.07, 95% CI = 2.35 to 4.01) and friends and acquaintances (k = 8, OR = 2.42, 95% CI = 1.50 to 3.91; Q = 0.77, df = 1, P = 0.38, R2
ð2Þ = 0%, R2
ð3Þ = 2.7%). No further significant moderators relating to study design charac-
teristics were identified (Table 2).
Table 1. (Continued )
Study, location,
study design
Exposed
population, mean
age or age range
(years), percent
female, total
sample size
Exposure Definition of exposure Outcome
(s)
Definition of outcome(s) Exposure ascertainment Study
quality
Mercy 2001 [28],
US, case–control
Youth, age
range = 13–35
(50.3% aged
�24), 54.5%
female, N = 666
Suicidal behavior
(composite) of
relative (any
relative); suicidal
behavior
(composite) of friend
or acquaintance
Self-report: Participants
were asked if their friends
or family had committed
suicide or made a suicide
attempt.
Suicide
attempt
Hospital admission
records: Hospital
admission for nearly
lethal suicide attempt,
defined as those in which
the person probably
would have died if they
had not received
emergency medical or
surgical intervention or in
which the attempter
unequivocally used a
method with a high case
fatality ratio (i.e., a gun or
a noose) and sustained an
injury, regardless of
severity.
All participants were
hospitalized for suicide
attempt at the time that
prior exposure was
measured.
Fair
a Psychological autopsy study.
b Majority of the population aged >24 years and therefore categorized as adults.
c Exposure was a composite measure of suicide in a relative or friend; however, the majority were exposed to a friend’s suicide.
d Exposure was a composite measure of suicidal behavior, but exposure to suicide was only 1%, and therefore the exposure was coded as exposure to suicide attempt.
ICD, International Classification of Diseases.
https://doi.org/10.1371/journal.pmed.1003074.t001
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Exposure to suicide attempt. Across 19 effect sizes from 13 studies, exposure to suicide
attempt was associated with 2.99-fold (95% CI = 2.19 to 4.09, P < 0.001; Fig 3) increased odds of suicidal behavior. Heterogeneity within studies was 9% (t2
ð2Þ = 0.022, I2
ð2Þ = 9%, 95% CI 1% to
54%), while heterogeneity between studies was substantially larger (t2 ð3Þ
= 0.22, I2 ð3Þ
= 88%, 95%
CI 42% to 97%). Inspection of the funnel plot did not reveal evidence of small study effect
(Egger’s intercept = −0.453, P = 0.33; S2 Fig). Results from subgroup analysis revealed that exposure to suicide attempt was associated with greater odds of subsequent suicide attempt
(k = 16, OR = 3.53, 95% CI = 2.63 to 4.73, P < 0.001) but not suicide death (k = 3, OR = 1.64, 95% CI = 0.90 to 2.98, P = 0.10; Q between subgroups = 4.22, df = 1, P = 0.04, R2
ð2Þ = 0%, R2
ð3Þ =
3.8%). Significant between-group differences were observed for study design, with cross-sec-
tional studies reporting greater odds of subsequent suicidal behavior (k = 2, OR = 8.23, 95% CI = 4.70 to 14.30, P < 0.001) compared to case–control studies (k = 10, OR = 2.74, 95% CI = 2.04 to 3.69, P < 0.001) and cohort studies (k = 7, OR = 2.69, 95% CI = 1.82 to 3.99, P < 0.001; Q between subgroups = 7.35, df = 2, P = 0.02, R2
ð2Þ = 0%, R2
ð3Þ = 72.8%). Finally, modera-
tor analyses revealed that psychological autopsy studies (k = 3, OR = 1.64, 95% CI = 0.90 to 2.99, P = 0.127) were associated with reduced odds of suicidal behavior compared to non-psy- chological autopsy studies (k = 16, OR = 3.53, 95% CI = 2.63 to 4.73, P < 0.001, Q-between subgroups = 4.22, df = 1, P = 0.03, R2
ð2Þ = 0%, R2
ð3Þ = 38.4%). No further significant differences
were observed for the remaining moderators (Table 3).
Exposure to suicidal behavior. Across 10 effect sizes from 5 independent studies, expo-
sure to suicidal behavior (composite measure—suicide or suicide attempt) was associated with
2.58-fold (95% CI = 1.25 to 5.35, P = 0.01) increased odds of suicidal behavior (Fig 4). Hetero- geneity within and between studies was comparable (t2
ð2Þ = 0.283 I2
ð2Þ = 38%; t2
ð3Þ = 0.40, I2
ð3Þ =
53%). Visual inspection of the funnel plot did not reveal evidence of small study effect (S3 Fig).
However, a formal test of asymmetry was not conducted due to insufficient studies. Results
from the subgroup analysis revealed that exposure to suicidal behavior was associated with
greater odds of suicide (k = 7, OR = 3.83, 95% CI = 2.38 to 6.17, P < 0.001) but not suicide attempt (k = 3, OR = 1.10, 95% CI = 0.69 to 1.76, P = 0.90; Q between subgroups = 5.02, df = 1, P = 0.02, R2
ð2Þ = 31.6%, R2
ð3Þ = 100%). The odds of suicidal behavior were also greater when the
exposure occurred in relatives (k = 8, OR = 3.09, 95% CI = 1.53 to 6.26, P = 0.001) compared to friends and acquaintances (k = 2, OR = 1.33, 95% CI = 0.69 to 2.92, P = 0.48; Q between sub- groups = 5.20, df = 1, P = 0.02, R2
ð2Þ = 86.2%, R2
ð3Þ = 0%). No significant differences were
observed for the remaining moderators (Table 4).
Discussion
Based on findings from 34 studies of mostly good and fair quality, encompassing 13,923,029
participants and 71 effect sizes, we found that prior exposure to suicide was associated with sig-
nificantly greater odds of suicidal behavior (suicide or suicide attempt; OR = 2.94). Results of
the moderator analysis revealed that prior exposure to suicide was associated with 3.23-fold
increased odds of suicide and 2.91-fold increased odds of suicide attempt, while there was no
evidence of an association between exposure to suicide and subsequent suicidal ideation.
These findings remained robust across cohort, case–control, and cross-sectional studies, as
well as exposure and outcome measurements encompassing informant interview, self-report,
and official records (e.g., coroner reports, hospital admission records, or data linkage with
birth and death registries).
Exposure to suicide attempt was associated with increased odds of suicidal behavior
(OR = 2.99). However, moderator analyses revealed that the association of exposure to suicide
PLOS MEDICINE Association of suicidal behavior with exposure to suicide and suicide attempt: A multilevel meta-analysis
PLOS Medicine | https://doi.org/10.1371/journal.pmed.1003074 March 31, 2020 14 / 27
attempt with suicide-related outcomes was significant only for suicide attempt (OR = 3.53),
not for suicide death (OR = 1.64). These findings were demonstrated across 19 effect sizes
from 13 studies of mostly fair quality, and corroborated by 3 large population-based studies
using data linkage or hospital admission records for suicide attempt [48,59,62]. Exposure to
suicidal behavior (suicide or suicide attempt) was associated with a 2.58-fold increased odds of
suicidal behavior, but moderator analysis revealed that this was significant only for outcomes
relating to suicide death (OR = 3.83), not suicide attempt (OR = 1.10). These findings were
demonstrated across 10 effect sizes from 5 studies, the majority of which involved psychologi-
cal autopsy methodologies.
Our analyses update and further specify the findings from previous systematic reviews,
which included estimates from studies reporting lifetime prevalence or did not differentiate
between the independent effects associated with exposure to suicide and exposure to suicide
attempt [19,22,23]. The finding that exposure to suicide was associated with an increased odds
of suicide and suicide attempt—in contrast to exposure to suicide attempt, which was associ-
ated with an increased odds of suicide attempt only—indicates that exposure to suicide and
suicide attempt do not incur uniform risk across the range of suicide-related outcomes. This
was corroborated by our analysis of exposure to suicidal behavior, which found that this com-
posite measure was associated with increased odds of suicide but not suicide attempt, a finding
that was inconsistent with our separate analyses of exposure to suicide and exposure to suicide
attempt. Taken together, the present findings raise questions about the conceptual value of
combining suicide and suicide attempt as a composite measure of suicidal behavior, and sug-
gest that future research and public health policies should refrain from combining these expo-
sures and outcomes into 1 composite measure of suicidal behavior.
Evidence from 2 studies [46,57] suggests that exposure to suicide may be associated with
increased risk of suicidal ideation, especially in older adults [46]. Conversely, results from a
single cohort study in youths [57] indicate higher risk for suicide attempt than for suicidal ide-
ation, pointing once more to lack of uniformity across populations and outcomes. Moreover,
theoretical and empirical accounts suggest that while exposure to suicide may contribute to
subsequent suicidal ideation to some extent, its effect on people with a history of suicidal idea-
tion may be more pronounced [71], as this experience might reduce cognitive and practical
barriers to acting on one’s suicidal thoughts [46,72,73]. A more comprehensive look at this
interaction may have important practical implications for developing specific interventions for
this high-risk population, in particular interventions guided by the “ideation-to-action frame-
work” [71] that aim to reduce acquired capability for suicidal behavior among individuals
exposed to suicide.
The increased risks associated with exposure to suicide for outcomes relating to suicide and
suicide attempt in the current meta-analyses suggest that further consideration should be
given towards developing interventions that target suicide-related outcomes in those bereaved
by suicide. To date, interventions targeting those exposed to suicide have largely focused on
bereavement-related factors such as grief, reduced social support, and stigma [74,75].
Although previous studies have shown that these factors are elevated among those bereaved by
suicide as opposed to other modes of death, there remains a dearth of studies that investigate
the effectiveness of interventions on suicide and suicide attempt behavior. A recent review by
Andriessen and colleagues [74], for example, found 3 controlled studies [76–78] that investi-
gated the effectiveness of an intervention on suicidal ideation and found no studies that
included outcomes related to suicide or suicide attempt.
Although we did not observe a significant association between exposure to suicide attempt
and subsequent suicide, the specific relationship between exposure to suicide attempt and sub-
sequent suicide attempt is noteworthy, since suicide attempt is associated with significant
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disruptions to an individual’s milieu, and has been linked to adverse psychosocial and mental
health stressors that persist later in life [5]. The findings from our analysis of exposure to
Fig 2. Forest plots of exposure to suicide and subsequent suicide, suicide attempt, and suicidal ideation outcomes.
CI, confidence interval; OR, odds ratio.
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suicide attempt also provide some insight into the mechanisms underlying the observed asso-
ciation between exposure to suicide and exposure to suicide attempt and the suicide-related
outcomes. Arguably, the absence of bereavement-related factors and the specific association
between exposure to suicide attempt and subsequent suicide attempt support the hypothesis
that suicidal individuals may model, or imitate, suicide-related behavior that they see in others
[10]. An imitation model is consistent with previous studies that have shown that increased
risk of suicide-related behavior following exposure to both suicide and suicide attempt is not
significantly moderated by preexisting risk factors such as depression, anxiety, and hospital
admission for mental health [79,80]. The finding that exposure to suicide is associated with sig-
nificant increased odds of suicide attempt is important since public health approaches for the
prevention of behavioral contagion of both suicide and suicide attempt, such as frameworks
for the prevention of suicide and self-harm clusters [12–15], have focused largely on mitigation
efforts following exposure to suicide and therefore may benefit from the inclusion of exposure
to suicide attempt in future mitigation efforts.
Limitations
The current systematic review and meta-analysis is the first to our knowledge to quantify the
association between exposure to suicide and suicide attempt and the full spectrum of suicide-
Table 2. Results of moderator analyses of exposure to suicide across suicide, suicide attempt, and suicidal ideation outcomes.
Moderator Number of effect sizes Odds ratio (95% confidence interval) P value R2(2) R 2
(3) ANOVA between-group P value Proximity
Relative 34 3.07 (2.35 to 4.01) <0.001
Friend or acquaintance 8 2.42 (1.50 to 3.91) <0.001 <0.001 0.03 0.38
Population at risk
Adult 24 2.80 (2.00 to 3.92) <0.001
Youth 18 3.04 (2.14 to 4.32) <0.001 <0.001 0.06 0.74
Outcome measurement
Informant interview 2 1.53 (0.63 to 3.73) 0.35
Official records 30 3.10 (2.30 to 4.17) <0.001
Self-report 10 2.97 (1.86 to 4.75) <0.001 0.04 0.04 0.34
Exposure measurement
Informant interview 7 3.53 (2.13 to 5.83) <0.001
Official records 20 2.84 (1.93 to 4.18) <0.001
Self-report 15 2.66 (1.78 to 3.97) <0.001 <0.01 <0.01 0.68
Psychological autopsy
No 34 2.64 (2.64 to 3.50) <0.001
Yes 8 3.71 (2.38 to 5.78) <0.001 0.03 0.07 0.21
Study design
Case–control 29 2.85 (2.14 to 3.80) <0.001
Cohort 10 2.13 (1.35 to 3.36) 0.01
Cross-sectional 3 4.98 (2.73 to 9.08) <0.001 <0.01 0.47 0.12
Study quality
Good 23 2.61 (1.86 to 3.67) <0.001
Fair 15 3.03 (2.13 to 4.30) <0.001
Poor 4 5.15 (1.97 to 13.48) <0.001 <0.001 0.09 0.41
ANOVA, analysis of variance.
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related outcomes and has many strengths, including the use of multilevel meta-analysis, the
large sample size, and the exclusion of estimates of lifetime prevalence that do not take into
account the temporal sequence between exposure and suicide-related outcomes. Despite this,
several limitations exist. Whilst we conducted an extensive search of 21,868 records, there is
the possibility that some relevant studies were not detected. Such studies are likely to create a
bias towards the null (i.e., the exposure not having a significant effect). This is a limitation that
is common to many systematic reviews and was mitigated to the best of our ability through
adherence to a screening protocol developed a priori.
Fig 3. Forest plots of exposure to suicide attempt and subsequent suicide and suicide attempt outcomes. CI, confidence
interval; OR, odds ratio.
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Furthermore, since most studies adjusted for different covariates, we restricted our analysis
to unadjusted events and ORs. Whilst this is consistent with previous meta-analyses in the
field [81,82], it meant that we could not investigate other risk factors, such as frequency of
exposure, duration since exposure, and baseline mental health diagnoses, and how these might
moderate the association between exposure to suicide and suicide attempt and suicide-related
outcomes. For example, a previous systematic review on pre- and post-loss features of suicide
bereavement in young people found evidence of a cumulative effect of exposure to suicide on
subsequent suicide risk [83]. In the present meta-analysis, 2 out of 34 studies included in our
analyses provided separate estimates for multiple exposures to suicide [62] and suicide attempt
[48]. In 1 study [62], exposure to 2 or more suicide deaths affected less than 1% of the popula-
tion, but was associated with 9.8-fold greater odds of suicide attempt, compared to an OR of
3.8 among those who had been exposed to the suicide of 1 relative. Similarly, those exposed to
the suicide attempt of 2 parents were 5.67 times more likely to make a suicide attempt, com-
pared to ORs of 2.89 and 3.89 (for paternal and maternal exposures, respectively) among
youths who had been exposed to the suicide attempt of 1 parent [48].
Indeed, in the present multilevel meta-analysis, within-study heterogeneity remained
largely unchanged by study-level moderators for both exposure to suicide and exposure to sui-
cide attempt. For example, we did not find evidence of a significant difference in suicide-
related outcomes when the exposure to suicide or suicide attempt occurred in relatives com-
pared to friends and acquaintances. Although previous registry-based studies have shown a
Table 3. Results of moderator analyses of exposure to suicide attempt across suicide, suicide attempt, and suicidal ideation outcomes.
Moderator Number of effect sizes Odds ratio (95% confidence interval) P value R2(2) R 2
(3) ANOVA between-group P value Proximity
Relative 14 3.14 (2.25 to 4.38) <0.001
Friend or acquaintance 5 2.64 (1.72 to 4.03) <0.001 0.14 <0.001 0.39
Population at risk
Adult 1 1.43 (0.48 to 4.32) 0.52
Youth 18 3.19 (2.35 to 4.32) <0.001 <0.001 0.16 0.18
Outcome measurement
Official records 10 2.60 (1.75 to 3.87) <0.001
Self-report 9 3.62 (2.30 to 5.68) <0.001 <0.01 0.13 0.29
Exposure measurement
Informant interview 3 1.64 (0.90 to 2.99) 0.12
Official records 5 3.60 (2.12 to 6.10) <0.001
Self-report 11 3.49 (2.45 to 4.98) <0.001 0.01 0.38 0.12
Psychological autopsy
No 16 3.53 (2.63 to 4.73) <0.001
Yes 3 1.64 (0.90 to 2.99) 0.13 <0.001 0.38 0.03
Study design
Case–control 10 2.74 (2.04 to 3.69) <0.001
Cohort 7 2.69 (1.82 to 3.99) <0.001
Cross-sectional 2 8.23 (4.70 to 14.30) <0.001 0.01 0.73 0.02
Study quality
Good 7 3.74 (2.20 to 6.30) <0.001
Fair 9 2.95 (1.93 to 4.50) <0.001
Poor 3 2.18 (1.10 to 4.32) 0.02 0.02 0.18 0.48
ANOVA, analysis of variance.
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6-fold increase of suicide among biological relatives of adoptees who have died by suicide [84],
in the present meta-analysis it was not possible to delineate between relatives who resided in
the same household, and therefore shared many of the same environmental risk factors, and
relatives who did not [9]. Understanding these factors is important for identifying specifically
who within in the general population is most at risk. However, the pooling of observational
studies meant that analyses of these factors were outside the scope of the present study. An
important next step forward would therefore be examinations of exposure to suicide and sui-
cide attempt while taking these risk factors into account using individual participant data
meta-analyses.
In the present multilevel meta-analysis, between-study heterogeneity remained moderate
(I2 ð3Þ
= 52.2%) across studies measuring exposure to suicide, which was not sufficiently
explained by any of the included study design moderators. By contrast, study design character-
istics accounted for 72.8% of between-study heterogeneity (I2 ð3Þ
= 87.8%) across studies measur-
ing exposure to suicide attempt. In this instance, cross-sectional studies reported significantly
larger ORs (OR = 8.23) compared to case–control (OR = 2.74) and cohort (OR = 2.69) studies.
In general, cross-sectional studies are prone to an inherently greater number of biases, com-
pared to case–control and cohort studies. This may be particularly pronounced in studies that
measure suicide attempt because recall of suicide attempt may be less salient than recall of sui-
cide death, and is prone to multiple interpretations and definitions [85].
It is noteworthy that we did not find evidence to support the role of age as a risk moderator,
as suggested in previous reviews [9,10]. Yet these results should be interpreted with caution, as
Fig 4. Forest plots of exposure to suicidal behavior (composite measure—suicide or suicide attempt) and subsequent
suicide and suicide attempt outcomes. CI, confidence interval; OR, odds ratio.
https://doi.org/10.1371/journal.pmed.1003074.g004
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the dichotomization of study populations into the categories of youths and adults was based
on a majority rule in 13 out of 34 studies [26–28,39,58,60,61,63–65,68–70]. The finding that
age was not a risk moderator may therefore be an artifact introduced by the imprecise age clas-
sification of the included population in individual studies. Furthermore, whilst similar patterns
were observed across studies examining exposure to suicide attempt in youths versus adults,
only 1 out of 13 studies [70] reported outcomes among adults, which may have impacted our
ability to detect a statistically significant difference.
Finally, the results of the present study do not allow causality to be inferred, and although
we show evidence of a temporal association between prior exposure to suicide and suicide
attempt and subsequent suicide-related outcomes, cross-sectional studies, by virtue of study
design, do not provide incidence estimates. To account for this limitation, we only included
cross-sectional studies where participants were explicitly asked about suicidal acts that
occurred after exposure to suicide or suicide attempt. But this approach does not mitigate
errors in recall and other biases that are inherently more common in cross-sectional studies.
Conclusions
Our findings suggest that prior exposure to suicide is associated with increased risk of suicide
and suicide attempt. By contrast, exposure to suicide attempt is associated with increased risk
of suicide attempt, but not suicide death. Future studies should refrain from combining sui-
cidal behaviors into composite measures of suicide exposures and outcomes as the relation-
ships between exposure to suicide and suicide attempt and suicide-related outcomes are
markedly different. Lastly, future studies should consider interventions that target suicide-
related outcomes in those exposed to suicide and include efforts to mitigate the adverse effects
associated with exposure to suicide attempt.
Table 4. Results of moderator analyses of exposure to suicidal behavior (composite measure—suicide or suicide attempt) across suicide, suicide attempt, and sui-
cidal ideation outcomes.
Moderator Number of effect sizes Odds ratio (95% confidence interval) P value R2(2) R 2
(3) ANOVA between-group P value Proximity
Relative 8 3.09 (1.53 to 6.26) 0.001
Friend or acquaintance 2 1.33 (0.60 to 2.92) 0.48 0.86 <0.001 0.02
Population at risk
Adult 4 2.63 (0.96 to 7.22) 0.06
Youth 6 2.53 (0.86 to 7.43) 0.09 <0.001 0.01 0.96
Outcome measurement
Informant interview 3 8.34 (2.35 to 29.63) 0.01
Official records 7 1.90 (1.03 to 3.50) 0.05 <0.01 0.70 0.07
Exposure measurement
Informant interview 7 3.83 (2.37 to 6.19) <0.001
Self-report 3 1.04 (0.59 to 1.83) 0.89 0.32 1 0.02
Psychological autopsy
No 3 1.04 (0.59 to 1.83) 0.89
Yes 7 3.83 (2.37 to 6.19) <0.001 0.32 1 0.02
Study quality
Fair 3 1.04 (0.59 to 1.83) 0.89
Poor 7 3.83 (2.37 to 6.19) <0.001 0.32 1 0.02
ANOVA, analysis of variance.
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Supporting information
S1 Data. Summary data for all included studies.
(XLS)
S1 Fig. Exposure to suicide funnel plot. The solid vertical lines indicate the 95% confidence
interval around the log odds ratio (LogOR). The dashed lines indicate the summary log odds
ratio ± 1.96 × standard error for each of the standard errors on the y-axis. The resulting trian- gular region indicates the expected location of 95% of studies in the absence of small study
effect.
(TIF)
S2 Fig. Exposure to suicide attempt funnel plot. The solid vertical lines indicate the 95% con-
fidence interval around the log odds ratio (LogOR). The dashed lines indicate the summary
log odds ratio ± 1.96 × standard error for each of the standard errors on the y-axis. The result- ing triangular region indicates the expected location of 95% of studies in the absence of small
study effect.
(TIFF)
S3 Fig. Exposure to suicidal behavior funnel plot. The solid vertical lines indicate the 95%
confidence interval around the log odds ratio (LogOR). The dashed lines indicate the summary
log odds ratio ± 1.96 × standard error for each of the standard errors on the y-axis. The result- ing triangular region indicates the expected location of 95% of studies in the absence of small
study effect.
(TIFF)
S1 Table. Description of a priori study moderators used for data extraction.
(DOCX)
S2 Table. Excluded overlapping studies.
(DOCX)
S3 Table. Risk of bias.
(DOCX)
S1 Text. PRISMA checklist.
(DOC)
S2 Text. MEDLINE search strategy.
(DOCX)
S3 Text. Articles excluded from the systematic review and meta-analysis.
(DOCX)
Author Contributions
Conceptualization: Nicole T. M. Hill, Jo Robinson, Allison Milner, Katrina Witt, Amit
Lampit.
Data curation: Nicole T. M. Hill, Karl Andriessen, Karolina Krysinska, Amber Payne, Alexan-
dra Boland, Alison Clarke, Katrina Witt, Stephan Krohn.
Formal analysis: Nicole T. M. Hill, Stephan Krohn, Amit Lampit.
Investigation: Nicole T. M. Hill, Karolina Krysinska, Stephan Krohn, Amit Lampit.
PLOS MEDICINE Association of suicidal behavior with exposure to suicide and suicide attempt: A multilevel meta-analysis
PLOS Medicine | https://doi.org/10.1371/journal.pmed.1003074 March 31, 2020 22 / 27
Methodology: Nicole T. M. Hill, Jane Pirkis, Karl Andriessen, Karolina Krysinska, Allison
Milner, Katrina Witt, Stephan Krohn, Amit Lampit.
Project administration: Nicole T. M. Hill.
Resources: Nicole T. M. Hill.
Software: Nicole T. M. Hill, Stephan Krohn, Amit Lampit.
Supervision: Nicole T. M. Hill, Jo Robinson, Jane Pirkis, Allison Milner, Amit Lampit.
Validation: Nicole T. M. Hill, Karl Andriessen, Karolina Krysinska, Amber Payne, Alexandra
Boland, Stephan Krohn, Amit Lampit.
Visualization: Nicole T. M. Hill, Stephan Krohn, Amit Lampit.
Writing – original draft: Nicole T. M. Hill, Jo Robinson, Jane Pirkis, Karl Andriessen, Karo-
lina Krysinska, Amber Payne, Alexandra Boland, Alison Clarke, Allison Milner, Katrina
Witt, Stephan Krohn, Amit Lampit.
Writing – review & editing: Nicole T. M. Hill, Jo Robinson, Jane Pirkis, Karl Andriessen, Kar-
olina Krysinska, Amber Payne, Alexandra Boland, Alison Clarke, Allison Milner, Katrina
Witt, Stephan Krohn, Amit Lampit.
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