Causal-Comparative Research

Presented by: zargham faramarzi

ex post facto means ‘from what is done afterwards.

In the context of social and educational research the phrase means ‘after the fact’ or ‘retrospectively’ and refers to those studies which investigate possible cause-and-effect relationships by observing an existing condition or state of affairs and searching back in time for plausible causal factors.

First use by chapin 1937 and green wood 1945

Definition

Imagine a situation in which there has been a dramatic increase in the number of fatal road accidents in a particular locality. An expert is called in to investigate. Naturally, there is no way in which she can study the actual accidents because they have happened; nor can she turn to technology for a video replay of the incidents. What she can do, however, is attempt a reconstruction by studying the statistics, examining the accident spots, and taking note of the statements given by victims and witnesses . In this way the expert will be in a position to identify possible determinants of the accidents. These may include excessive speed, poor road conditions, careless driving, frustration, inefficient vehicles, the effects of drugs or alcohol and so on. On the basis of her examination, she can formulate hypotheses as to the likely causes and submit them to the appropriate authority in the form of recommendations. These may include improving road conditions, or lowering the speed limit, or increasing police surveillance, for instance. The point of interest to us is that in identifying the causes retrospectively, the expert adopts an ex post facto perspective.

Example

Characteristics of Ex Post Facto• The independent variable (IV) is not

manipulated; it has already occurred.• Less costly and time-consuming to conduct.• Establishing cause-effect relationships is

more difficult than in experiments.• Researcher has little to no control over

independent variables.• Flexible by nature.

Examples of non-manipulated independent variables

• Age• Sex

• “Learning style”• Socioeconomic status (SES)

• Parent educational level• Family environment

• Type of school attended

When to use this?

• You can use this where more powerful experimental designs are not possible; when you are unable to select, control and manipulate the factors necessary to study cause and effect relationships directly, or when control variables except a single independent variable may be unrealistic and artificial.

Ex post facto advantages and disadvantages

Advantages• Show a correlation where

more rigorous experimentation is not possible

• Exploratory tool• Useful to avoid artificial in

the research.• Shows cause and effect

relationships (possible)

Disadvantages• Lack of control for

independent variable and randomizing subjects.

• Never certain if causative factor has been included or identified

• Relationship between two factors does not est. cause and effect.

• May be regarded as too flexible.

Steps Involved in Causal-Comparative Research

• Problem Formulation• The first step is to identify and define the particular phenomena of interest

and consider possible causes• Sample

• Selection of the sample of individuals to be studied by carefully identifying the characteristics of select groups

• Instrumentation• There are no limits on the types of instruments that are used in Causal-

comparative studies• Design

• The basic design involves selecting two or more groups that differ on a particular variable of interest and comparing them on another variable(s) without manipulation .

McGraw-Hill © 2006 The McGraw-Hill Companies, Inc. All rights reserved.

The Basic Causal-Comparative DesignsIndependent Dependent

Group variable variable(a) I C O

(Group possesses (Measurement)characteristic)

II –C O(Group does (Measurement)not possess

characteristic)

(b) I C1 O(Group possesses (Measurement)characteristic 1)

II C2 O(Group possesses (Measurement)characteristic 2)

McGraw-Hill © 2006 The McGraw-Hill Companies, Inc. All rights reserved.

Ways to control in Causal-Comparative Research

One way to control for an extraneous variable is to match subjects from the comparison groups on that variable

Creating or finding homogeneous subgroups would be another way to control for an extraneous variable

The third way to control for an extraneous variable is to use the technique of statistical matching

covariance

McGraw-Hill © 2006 The McGraw-Hill Companies, Inc. All rights reserved.

Threats• Loss of subjects• Location• Instrumentation• History• Maturation

• Data collector bias• Instrument decay• Attitude• Regression• Pre-test/treatment

interaction effect

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

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

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