The
Practice of Social Research
Chapter Outline
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Topics Appropriate to Experiments
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The
Classical Experiment
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Selecting Subjects
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Variations on Experimental Design
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An
Illustration of Experimentation
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Alternative Experimental Settings
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Strengths and Weaknesses of the Experimental Method
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Ethics and Experiments
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Quick Quiz
Experiments
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Experiments involve:
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Taking action
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Observing consequences of that action
Topics Appropriate to Experiments
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Well-suited for projects involving limited and well-defined concepts and
propositions.
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Hypothesis testing
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Better suited for explanatory than descriptive
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Small group interaction
The Classical Experiment
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Major Components
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Independent and Dependent Variables
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Pre-testing and Post-testing
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Experimental and Control Groups
The Classical Experiment
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Independent and Dependent Variables
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Independent – takes the form of a stimulus (present or absent), cause
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Dependent - effect
The Classical Experiment
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Pre-testing – the measurement of a dependent variable along subjects.
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Post-testing – the measurement of a dependent variable among subjects after they
have been exposed to an independent variable.
The Classical Experiment
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Experimental Group – a group of subjects to whom an experimental stimulus is
administered.
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Control Group – a group of subjects to whom no experimental stimulus is
administered and who should resemble the experimental group in all other
respects.
The Classical Experiment
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The
Double-Blind Experiment – an experimental design in which neither the subjects
nor the experimenters know which is the experimental and which is the control
group.
Selecting Subjects
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Role of college students
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Generalizability?
Selecting Subjects
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Probability Sampling
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Randomization – a technique for assigning experimental subjects to experimental
and control groups.
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Matching – the procedure whereby pairs of subjects are matched on the basis of
their similarities on one or more variables, and one member of the pair is
assigned to the experimental group and the other to the control group.
Variations on Experimental Design
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Pre-experimental Research Designs
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One-shot case study – a single group of subjects is measured on a dependent
variable following an experimental stimulus.
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One-group pre-test post-test design – a pre-test is added for the experimental
group but lacks a control group.
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Static-group comparison – includes experimental and control groups, but no
pre-test.
Variations on Experimental Design
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Validity Issues in Experimental Research
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Internal Validity – the possibility that conclusions drawn from experimental
results may not accurately reflect what happened in the experiment itself.
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Sources: history, maturation, testing, instrumentation, statistical regression,
selection bias, experimental mortality, causal time order, diffusion or
imitation of treatments, compensation, compensatory rivalry, demoralization
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External Validity – the possibility that conclusions drawn from experimental
results may not be generalizable to the “real” worl
Alternative Experimental Settings
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Web-Based Experiments
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“Natural” Experiments
Strengths and Weaknesses of the Experimental Method
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Strengths of Experimental Method
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Isolation of experimental variable’s impact over time.
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Replication
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Weaknesses of Experimental Method
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Artificiality of laboratory settings