Experimental Design Causal Effect The finding that change

Experimental Design

Causal Effect • The finding that change in one variable leads to change in another variable, ceteris paribus (other things being equal)

Hypothesis? Do individuals who view a violent videotape act more aggressively than individuals who view a nonviolent video tape?

Experimental Research • Population? • Assignment? • Dependent Variable? • Independent Variable?

Conditions Necessary for Determining Causality 1. Empirical Association 2. Appropriate Time Order 3. Nonspuriousness Conditions Important in Specifying Causal Relationships 1. Mechanism 2. Context

Mean Noise Intensity by Type of Videotape

2 X 2 Factorial Design Violent Non-Violent Predisposed Yes X X No X X

Time Order Violence on Television Violent Crime Commit Violent Crime Watch Violence on Television

Spurious Relationship View the movie Money Train Feel enraged against society Commit violent crime View the movie Money Train Commit violent crime

True Experiments 1. Two comparison groups 2. Random assignment 3. Assessment of change in the dependent variable

Classical Experimental Design R O O X O O

Quasi-Experimental Design Nonequivalent Control Group Experimental: O 1 Comparison: O 1 X O 2 Experimental Pretest X Posttest Comparison Pretest Posttest

Percentage of Drivers Using Seat Belts