This document summarizes causal-comparative (ex post facto) research, which attempts to identify cause-and-effect relationships after the fact by comparing two or more groups that differ on an independent variable. Key features include the independent variable already occurring and not being manipulated. It is more difficult than experiments to establish causation. Procedures involve identifying a condition, looking back for potential causes, and ruling out other factors. Examples compare groups that differ in age, sex, SES, etc. Interpreting findings requires caution due to alternative explanations. The document also summarizes a study comparing students who did and did not receive a Follow-Through intervention program.

1. Group Comparison Research
CAUSAL-COMPARATIVE
(EX POST FACTO)
RESEARCH
BY:
DR RAKHI SAWLANI

2. Purpose
 Attempts to determine cause for
 Existing conditions
 Preexisting differences in groups
 Alleged cause and effect have already occurred
 Orientations
 Retrospective (basic): starts with an effect and seeks
possible causes
 Prospective (variation): starts with a cause and
investigates its effects on some variable

3. Features
 The independent variable (IV) is not
manipulated; it has already occurred
 Independent variables sometimes
called “attribute variables”
 Less costly and time-consuming to
conduct
 Establishing cause-effect relationships
is more difficult than in experiments

4. Procedures
 Identify an existing condition /event
 (e.g., differences in socialization among
1st grade students)
 Look “backwards” to see what may
have caused this difference /condition
to occur
 (i.e., some attended preschool, some
did not)
 Rule out other causal factors

6. Sometimes confused with
correlational research:
 Both lack manipulation of variables
 Both require caution in interpreting
results
 Both can support subsequent
experimental research

7. Causal comparative vs.
Correlational research
 Causal comparative
 Attempts to identify
cause-effect
relationships
 At least one
independent variable
 Two or more groups
 Involves a comparison
 Correlational
 No attempt to
understand cause and
effect
 Two or more variables
 Only one group

8. Sometimes confused with
experimental research:
 Both try to establish cause-effect
relationships
 Both can test hypotheses concerning the
relationship between an independent (X)
and a dependent variable (Y)
 Both involve group comparisons

9. Comparison to experiments
 Causal comparative
 Individuals already in
groups before study
begins
 Independent variable
has already occurred
 Independent variable
is not manipulated
 Cannot be
 Should not be
 Could be, but is not
 Experiment
 Individuals
randomly assigned
to groups (e.g.,
treatment or
control)
 Independent
variable
manipulated by
the researcher

10. Examples of non-manipulated
independent variables
 Age
 Sex
 Ethnicity
 “Learning style”
 Socioeconomic status (SES)
 Parent educational level
 Family environment
 Type of school attended

11. Design of causal-comparative
research
 Select 2 groups that differ on some IV
 One group possesses a characteristic that the
other does not
 Each group possesses the characteristic, but in
differing amounts
 Randomly sample Ss from each group
 Collect info on Ss to determine equality of
the groups
 Compare groups on the DV

12. Difficulty in interpreting
findings
 Establishing cause and effect requires
caution!
 Alternative explanations:
Different causal variable
Order of causation
Reverse causality
Order of occurrence

13. Evidence necessary to
demonstrate that X causes Y:
 Establish statistical relationship
between X and Y (i.e., correlational
research);
 determine that X precedes Y in time
(collect data over time, i.e.,
longitudinal research);
 demonstrate that other, unknown
factors did not determine the
dependent variable (i.e.,
experimental research).

14. Becker & Gersten (1982): “Effects of
Project Follow-Through…”
 Quasi-experimental study
 Ex post facto study
 Problem: Are the two groups in
this study comparable to one
another?

15. In order to make sure that the two groups are
comparable, and to ensure that the only post-test
differences between the groups are due to the
independent variable (the Follow-Through
intervention), data were obtained on students’:
family income
gender
language spoken in home
mother’s education
ethnicity
number of siblings.

16. Research Design
 FOLLOW-THROUGH
 Year 1 (1975) Gr 5
 Site 1
 Site 2
 Site 3
 Site 4
 Site 5
 Year 2 (1976) Gr 6
 Site 1
 Site 2
 Site 3
 Site 4
 Site 5
 NO FOLLOW-THROUGH
 Year 1 (1975) Gr 5
 Site 1
 Site 2
 Site 3
 Site 4
 Site 5
 Year 2 (1976) Gr 6
 Site 1
 Site 2
 Site 3
 Site 4
 Site 5

17. Dependent variables
 Wide-Range Achievement Test (WRAT)
reading
mathematics
 Metropolitan Achievement Test (MAT)
reading
mathematics

18. RESULTS
 A total of 180 comparisons of FT to
No-FT students. Of these, only 56
(31%) favored FT students!
 Largest differences between FT and
No-FT students were in basic skills
areas.
 FT students’ achievement declined
by grades 5 and 6 (2-3 years after
end of FT).

19. Critique of this research
 What are the strengths of the study?
 Groups are comparable to one another.
 Contrasted statistical with practical significance.
 Large sample size.
 Multiple “replications” of treatment effect.
 What are the weaknesses of the study?
 Lack of random assignment.
 Focus on standardized test performance.