Statistics for the Social Sciences Psychology 340 Spring 2005 Factorial ANOVA

Statistics for the Social Sciences Outline Basics of factorial ANOVA –Interpretations Main effects Interactions –Computations –Factorial ANOVA in SPSS –Assumptions, effect sizes, and power –Other Factorial Designs More than two factors Within factorial ANOVAs

Statistics for the Social Sciences Outline Basics of factorial ANOVA –Interpretations Main effects Interactions –Computations –Factorial ANOVA in SPSS –Assumptions, effect sizes, and power –Other Factorial Designs More than two factors Within factorial ANOVAs

Statistics for the Social Sciences Statistical analysis follows design The factorial (between groups) ANOVA: –More than two groups –Independent groups –More than one Independent variable

Statistics for the Social Sciences Factorial experiments Two or more factors –Main effects - the effects of your independent variables ignoring (collapsed across) the other independent variables –Interaction effects - how your independent variables affect each other B1B2B3 A1 A2

Statistics for the Social Sciences Partitioning the variance Total variance Stage 1 Between groups variance Within groups variance Stage 2 Factor A varianceFactor B varianceInteraction variance

Statistics for the Social Sciences Factorial ANOVA in SPSS Go through how to set up SPSS to conduct a factorial ANOVA Factor A: Study Method CrammedDistributed Factor B: Subject Math74, 81, 93, 84, 7289, 80, 74, 84, 83 English Lit 62, 66, 72, 81, 7884, 81, 89, 84, 96

Statistics for the Social Sciences Effect Size in Factorial ANOVA

Statistics for the Social Sciences Approximate Sample Size Needed in Each Cell for 80% Power (.05 significance level)

Statistics for the Social Sciences Factorial ANOVA in Research Articles A two-factor ANOVA yielded a significant main effect of voice, F(2, 245) = 26.30, p <.001. As expected, participants responded less favorably in the low voice condition (M = 2.93) than in the high voice condition (M = 3.58). The mean rating in the control condition (M = 3.34) fell between these two extremes. Of greater importance, the interaction between culture and voice was also significant, F(2, 245) = 4.11, p <.02.

Statistics for the Social Sciences Extensions and Special Cases of the Factorial ANOVA Three-way and higher ANOVA designs Repeated measures ANOVA

Statistics for the Social Sciences Recruiting Looking for a teaching experience? Enjoy (tolerate?) statistics Dr. Jef Kahn is looking for Undergraduate Teaching Assistant(s) for PSY 340 next semester If interested: 1.He’ll be by at the end of class today 2. him about your interest: