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Causal - Comparative Research

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on 18 February 2014

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Transcript of Causal - Comparative Research

Causal - Comparative Research
Steps Involved in Causal - Comparative Research
Threats to Internal Validity
in Causal-Comparative Research
Two Weaknesses:
lack of randomization
inability to manipulate

by Büşra Demir & Delal K. Demir
What is Causal - Comparative Research?
Investigators attempt to determine
the cause
or
consequences of
differences that ALREADY
exist
between or among groups of individuals.
the
reason for

OR

the
results of
a difference
The difference has already been occurred.
Causal - comparative research is also referred to sometimes as
"ex post facto"
(from the Latin for
"after the fact"
) research.
Much of the research in medicine and sociology is causal - comparative in nature. (because of the ethical reasons)
Types of Causal - Comparative Research
Type 1:
Exploration of effects (dependent variable) caused by membership in a given group
Question:
What differences in abilities are caused by gender?
Research hypothesis:
Females have a greater amount linguistic ability than males.
Type 2:
Exploration of causes (independent variable) of group membership
Question:
What causes individuals to join a gang?
Research hypothesis:
Individuals who are members of gangs have more aggressive personalities than individuals who are not members of gangs.
Type 3:
Exploration of the consequences (dependent variable) of an intervention
Question:
How do students taught by the inquiry method react to propaganda?
Research hypothesis:
Students who were taught by the inquiry method are more critical of propaganda than others.
Causal - Comparative Research
Example:
A researcher is interested in the reason(s) why some individuals become addicted to
alcohol
while others develop a dependence on
pills
.
Problem Formulation
identify and define the particular phenomena of interest
consider / speculate possible causes for, or consequences of, these phenomena
incorporate the possible causes into a more precise statement
Sample
define carefully the characteristics to be studied and then select groups that differ in this characteristics
form reasonably homogenous groups
match the defined groups on one or more variables
Instrumentation
no limits on the types of instruments that may be used:
- achievement tests,
- questionnaires,
- interview schedules,
- attitudinal measures,
- observational devices,
- etc.
Design
Subject Characteristics
Matching of Subjects
Finding or Creating
Homogenous Groups
Statistical Matching
Other Threats
Evaluating Threats to Internal Validity
in Causal-Comparative Studies
Step 1: What specific factors either are known to affect or may logically be expected to affect the variable on which groups are being compared?
Step 2: What is the likelihood of the comparison groups differing on each of these factors?
Step 3: Evaluate the threats on the basis of how likely they are to have an effect, and plan to control for them.
Possible causes of student dropping out in inner-city high schools.
Hypotheses:
1. Family Instability
2. Low Student Self-esteem
3. Lack of a support system
Subject Characteristics:
1. Socioeconomic level of the family
2. Gender
3. Ethnicity
4. Marketable job skills
Mortality
Location
Other Threats
Construct frequency polygons
Calculate means and standard deviations
T-test to show differences between means
The result do not prove cause and effect, but only identifying the relationship

Data Analysis
Does a Threat to Internal Validity Exist?
Full transcript