DRAFT PURPOSE STATEMENT INSTRUCTIONS

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Chapter 4:

General Issues in Research Design

Learning Objectives

• Recognize how explanatory scientific research centers on the notion of cause and effect, and why this is a probabilistic model of causation

• Describe the three basic requirements for establishing a causal relationship in science, together with what is a necessary cause and a sufficient cause

• Understand the role of validity and threats to validity of causal inference

• Summarize the four classes of validity threats, and how they correspond to questions about cause and effect

Learning Objectives, cont.

• Discuss how a scientific realist approach bridges idiographic and nomothetic approaches to causation

• Describe different units of analysis in criminal justice research

• Explain how the ecological fallacy relates to units of analysis

• Understand the time dimension, together with the differences between cross-sectional and longitudinal research

• Describe how retrospective studies may approximate longitudinal studies

Introduction

• Causation, units, and time are key elements in planning a research study

• As social scientists, we seek to explain the causes of some phenomenon (e.g., crime)

• Who or what we are studying is an important part of research

• Researchers also must consider the time order of events

Causation in the Social Sciences

• Causation is the focus of explanatory research • Cause in social science is inherently

probabilistic – Certain factors make crime/delinquency more or less likely

within groups of people – Two models of explanation

• Ideographic: Lists the many, perhaps unique considerations behind an action

• Nomothetic: Lists the most important (and fewest) considerations/variables that best explain general patterns of cause and effect

Criteria for Causality

• Posited by Shadish, Cook, & Campbell (2002) – Empirical relationship between variables

– Temporal order (cause precedes effect)

– No alternative explanations—no spurious other variable(s) affecting the initial relationship

• Any relationship that satisfies all these criteria is causal

Necessary and Sufficient Causes

• Within the probabilistic model, two types: – Necessary cause: Represents a condition that must be present

for the effect to occur (e.g., being charged is necessary cause to be convicted)

– Sufficient cause: Represents a condition that, if it is present, will pretty much guarantee that the effect will occur (e.g., pleading guilty is sufficient cause to being convicted)

Validity and Causal Inference

• Scientists assess the truth of statements about cause by considering threats to validity

• When we make a cause-and-effect statement, we are concerned with its validity—whether it is true and valid

• Certain threats to the validity of our inference exist

• These are reasons why we might be incorrect in stating that some cause produces some effect

Discussion Question 1

What are the greatest threats to validity in social science?

Statistical Conclusion Validity

• Refers to our ability to determine whether a change in the suspected cause is statistically associated with a change in the suspected effect

• Are two variables related to each other? • Researchers cannot have much confidence in

statements about cause if their findings are based on a small number of cases

Internal Validity

• An observed association between two variables has internal validity if the relationship is, in fact, causal and not due to the effects of one or more other variables

• Generally due to nonrandom or systemic error • The threat to IV results when the relationship between

two variables arises from the effect of some third variable – Example: drug users sentenced to probation over prison recidivate less

Discussion Question 2

How can you best set up an experiment with strong internal validity?

External Validity

• Concerned with whether research findings in one study can be replicated in another study, often under different conditions

• Do the findings apply equally in different settings (locales, cities, populations)?

• Kansas City evaluation found sharp reductions in gun-related crimes in hot spots that had been targeted for focused police patrols – Indianapolis and Pittsburgh launched similar projects

Construct Validity

• Concerned with how well an observed relationship between variables represents the causal process

• Refers to generalizing from what we observe and measure to the real-world things in which we are interested – e.g., close supervision of officers -> more tickets?

– e.g., Kansas City Preventive Patrol Experiment, “police visibility”

Validity & Causal Inference Summarized

• The four types of validity threats can be grouped into these two categories

• Bias: Internal Validity and Statistical Conclusion Validity threats are related to systematic and nonsystematic bias

• Generalizability: Construct Validity and External Validity are concerned with generalization to real-world behaviors and conditions

Discussion Question 3

What if someone offered you a survey taken by South Africans to help you with your survey project for North Americans? Would you have any reservations as a social scientist?

Does Drug Use Cause Crime?

• Temporal order: which comes first? • A statistical relationship exists, but

underlying causes affect both drug use and crime (Internal Validity threat)

• What constitutes drug use? Crime? (Construct Validity threat)

• How will policy affect drug use and crime? – A crackdown on all drugs among all populations will do

little to reduce serious crime

Introducing Scientific Realism

• Bridges idiographic and nomothetic approaches to explanation by seeking to understand how causal mechanisms operate in specific contexts – Studies how such influences are involved in cause-and-

effect relationships – Exhibits both ideographic & nomothetic approaches to

explanation – "Can the design of streets and intersections be modified

to make it more difficult for street drug markets to operate?"

Units of Analysis

• What or who is studied – Individuals: Police, victims, defendants, inmates, gang

members, burglars, etc. – Groups: Multiple persons with same characteristics

(gangs, cities, counties, etc.) – Organizations: Formal groups with established leaders

and rules (prisons, police departments, courtrooms, drug treatment facilities, etc.)

– Social artifacts: Products of social beings and their behavior (stories in newspapers, posts on the Internet, photographs of crime scenes, incident reports, police/citizen interactions)

Issues of Logic • Ecological fallacy: Danger of making assertions

about individuals based on the examination of groups or aggregations – Poor areas = more crime, therefore poor people commit more

crime

• Individual fallacy: Using anecdotal evidence to make an argument – O.J. Simpson court resources

• Reductionism: Failing to see the myriad of possible factors causing the situation being studied

The Time Dimension

• Time sequence is critical in determining causation

• Time is also involved in the generalizability of research findings

• Observations can either be made more or less at one point, or stretched over a longer period – Observations made at more than one time point can

look forward or backward

Cross-Sectional Studies

• Observing a single point in time (cross-section) • Simple and least costly way to conduct

research • Typically descriptive or exploratory in nature • A single wave of the National Crime

Victimization Survey (NCVS) is a descriptive cross-sectional study that estimates how many people have been victims of crime in a given time

Longitudinal Studies

• Permit observations over time – Trend: Those that study changes within some

general population over time (UCR) – Cohort: Examine more specific populations as they

change over time (Wolfgang study) – Panel: Similar to trend or cohort, but the same set of

people is interviewed on two or more occasions (NCVS, panel attrition)

Approximating Longitudinal Studies

• Gun ownership and violence study by Swiss researcher Martin Killias (1993) – Compared rates of gun ownership as reported in an international

crime survey to rates of homicide and suicide committed with guns

• May be possible to draw approximate conclusions about processes that take place over time, even when only CS data is available

• When time order of variables is clear, logical inferences can be made about processes taking place over time

Retrospective Research • Asks people to recall their past for the

purpose of approximating observations over time

• People have faulty memories; people lie • Analysis of past records also suffer from

problems—records may be unavailable, incomplete, or inaccurate

• Prospective research: longitudinal study that follows subjects forward in time (Widom, child abuse/drug use)

Time Dimension Summarized

• Cross-sectional study = snapshot: an image at one point in time

• Trend study = slide show: a series of snapshots in sequence over time, allows us to tell how some indicator varies over time

• Panel study = motion picture: gives information about individual observations over time