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).

Investigate

Differing on the independent variable:Presence of independent variableAbsence of independent variableDegrees of independent variable

Effect on the dependent variable

Same on the independent variable(s)

Effect on the dependent variable

EX POST FACTO RESEARCH AND INDEPENDENT VARIABLES

Investigate

Differing on independent variables:Presence of independent variablesAbsence of independent variablesDegrees of independent variables

Same on the dependent variable

EX POST FACTO RESEARCH AND DEPENDENT VARIABLES

Differing on the dependent variable

Investigate

Differing on independent variables:Presence of independent variablesAbsence of independent variablesDegrees of independent variables

Investigate

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

Effective teaching

Ineffective teaching

EFFECT POSSIBLE CAUSE

Presence of collegial curriculum planning

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 causal-comparative.

• 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.