causalcomparative

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.