EXPERIMENTAL RESEARCH

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# EXPERIMENTAL RESEARCH - PowerPoint PPT Presentation

EXPERIMENTAL RESEARCH. How do you establish causality? what causes something else to occur? Lazarsfeld provided three criteria: 1. Covariation – two are related 2. Time order – cause before outcome 3. Elimination of likely third variables. Establishing causality.

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Presentation Transcript
EXPERIMENTAL RESEARCH

How do you establish causality?

• what causes something else to occur?
• Lazarsfeld provided three criteria:
• 1. Covariation – two are related
• 2. Time order – cause before outcome
• 3. Elimination of likely third variables
Establishing causality
• Surveys allow you to test for covariation.
• Statistical techniques “control” for third variables
• But experiments offer control over timing
• Manipulate the Independent Variable and observe the consequences (the Dependent Variable).
• Select a group of subjects
• Do something to them
• Observe the effects
Examples of causality questions
• Night lights
• The “Mozart effect”

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VARIABLES: Independent and Dependent
• CAUSE
• Independent variable
• OUTCOME
• Dependent variable

CAUSE

OUTCOME

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A “classic” experiment
• Independent and Dependent variables
• Experimental and Control groups
• exposed and non-exposed
• Pre-testing and Post-testing
• measure attitudes toward product and sales
• "Blind" to condition
• Hawthorne effect, placebo effects
Experiments

Selecting subjects

• Randomization
• equal chance of being in control or experimental condition
• random number table, even-odd, etc.
• Matching
• equalizing "important" variables
• age, education, product use, etc.
Experiments

External validity

• (How generalizable are the findings?)
• artificiality of the situation
• the lab setting, white lab coat, etc.
• sampling issues
• reliance on college students in experiments
Experimental design

Basic

• O- X - O experimental group
• O - . - O control group
Experimental design

Solomon 4-group:

O- X - O experimental group (pretest-posttest)

O - . - O control group (pretest-posttest)

. X - O posttest-only experimental group

. . - O posttest-only experimental group

• attempts to assess sensitization

(from pretesting)

Experimental design

“Factorial” designs

Multiple variables are examined

• Number of factors
• One factor (involvement)
• Two factors (involvement and gender)
• Number of “levels” for each factor
• e.g., 2 by 2 design…
• or 2 (involvement) by 2 (gender) design…

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### The End

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