EX POST FACTO
RESEARCH
© LOUIS COHEN, LAWRENCE MANION
& KEITH MORRISON
STRUCTURE OF THE CHAPTER
•
•
•
•
Co-relational and criterion groups designs
Characteristics of ex post facto research
Occasions when appropriate
Advantages and disadvantages of ex post facto
research
• Designing an ex post facto investigation
• Procedures in ex post facto research
TWO APPROACHES TO EX POST
FACTO RESEARCH
1. One commences with subjects who differ on
an independent variable, for example their
years of study in mathematics, and then
study how they differ on the dependent
variable, e.g. a mathematics test.
2. One commences with subjects who differ on
the dependent variable (for example their
performance in a mathematics test) and
discover how they differ on a range of
independent variables, e.g. their years of
study, their liking for the subject, the amount
of homework they do in mathematics).
EX POST FACTO RESEARCH AND
INDEPENDENT VARIABLES
Differing on the independent variable:
Presence of independent variable
Absence of independent variable
Degrees of independent variable
Investigate
Effect on the dependent variable
Same on the independent variable(s)
Investigate
Effect on the dependent variable
EX POST FACTO RESEARCH AND
DEPENDENT VARIABLES
Differing on the dependent variable
Investigate
Differing on independent variables:
Presence of independent variables
Absence of independent variables
Degrees of independent variables
Same on the dependent variable
Investigate
Differing on independent variables:
Presence of independent variables
Absence of independent variables
Degrees of independent variables
CO-RELATIONAL AND CRITERION
GROUP STUDY
• Co-relational study (causal research):
– to identify the antecedents of a present condition.
– collect two sets of data, one of which will be
retrospective, with a view to determining the
relationship between them.
• Criterion group study (causal-comparative
research):
– to discover possible causes for a phenomenon
being studied.
– Compare the subjects in which the variable is
present with similar subjects in whom it is absent.
TWO CAUSES AND TWO EFFECTS
IN CRITERION GROUP STUDY
EFFECT
POSSIBLE CAUSE
Effective
teaching
Presence of collegial
curriculum planning
Ineffective
teaching
Absence of collegial
curriculum planning
Two criterion groups:
(a) Presence of collegial planning
(b) Absence of collegial planning
CHARACTERISTICS OF EX POST
FACTO RESEARCH
• In ex post facto research the researcher takes
the effect (or dependent variable) and
examines the data retrospectively to establish
causes, relationships or associations, and
their meanings.
EX POST FACTO RESEARCH IS
USEFUL WHEN . . .
• It is impossible, impractical, costly or
unethical to conduct an experiment.
• It is not possible to select, control and
manipulate the factors necessary to study
cause-and-effect relationships directly.
• When the control of all variables except a
single independent variable may be
unrealistic and artificial.
• Where the independent variable lies outside
the researcher’s control.
ADVANTAGES OF EX POST
FACTO RESEARCH
• Useful where the more rigorous experimental
approach is not possible.
• Useful to study what goes with what and
under what conditions.
• Useful where the setting up of the latter would
introduce a note of artificiality into research
proceedings.
• Useful where simple cause-and-effect
relationships are being explored.
• It can give a sense of direction and provide a
source of hypotheses that can subsequently
be tested by the more rigorous experimental
method.
DIFFICULTIES IN EX POST FACTO
RESEARCH
• Direction of causality difficult to establish: what
caused what.
• Lack of control of the independent variable or
variables.
• Impossible to isolate and control every possible
variable, or to know with absolute certainty which
are the most crucial variables.
• Randomization impossible.
• Can provide support for any number of different,
even contradictory, hypotheses.
• Correlation does not equal cause.
• Lack of control: the researcher cannot
manipulate the independent variable or
randomize her subjects.
DISADVANTAGES OF EX POST
FACTO RESEARCH
• One cannot know for certain whether the causative
factor has been included or even identified.
• It may be that no single factor is the cause.
• A particular outcome may result from different
causes on different occasions.
• It is not possible to disconfirm a hypothesis.
• Classifying into dichotomous groups can be
problematic.
• As the researcher attempts to match groups on key
variables, this leads to shrinkage of sample.
• Conclusions may be based on too limited a sample
or number of occurrences.
• It may fail to single out the really significant factor(s).
DESIGN AND PROCEDURES IN AN
EX POST FACTO INVESTIGATION
1. Identify the problem area to be investigated.
2. Formulate a hypothesis to be tested or questions to be
answered.
3. Make explicit the assumptions on which the hypothesis
and subsequent procedures will be based.
4. Review of the research literature will follow to ascertain
the kinds of issues, problems, obstacles and findings
disclosed by previous studies in the area.
5. Plan the actual investigation:
– identify the population and samples;
– select and construct techniques for collecting data;
– establish categories for classifying the data.
6. Describe, analyse and interpret the findings.
DESIGN AND PROCEDURES IN AN
EX POST FACTO INVESTIGATION
Stage One: Define the problem and survey the
literature.
Stage Two: State the hypotheses and the
assumptions or premises on which the
hypotheses and research procedures are
based.
Stage Three: Select the subjects (sampling)
and identify the methods for collecting the data.
Stage Four: Identify the criteria and categories
for classifying the data to fit the purposes of the
study.
DESIGN AND PROCEDURES IN AN
EX POST FACTO INVESTIGATION
Stage Five: Gather data on those factors which are
always present in which the given outcome occurs,
and discard the data in which those factors are not
always present.
Stage Six: Gather data on those factors which are
always present in which the given outcome does
not occur.
Stage Seven: Compare the two sets of data (i.e.
subtract the former (Stage Five) from the latter
(Stage Six), in order to infer the causes that are
responsible for the occurrence or non-occurrence of
the outcome.
Stage Eight: Analyze, interpret and report findings.
CONTROLS IN EX POST FACTO
RESEARCH
• Match the subjects in the experimental and
control groups where the design is causalcomparative.
• Build the extraneous independent variables
into the design and then use an analysis of
variance technique.
• Select samples that are as homogeneous as
possible on a given variable.
• State and test alternative hypotheses that
might be plausible explanations for the
empirical outcomes of the study.