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Statistics for the Social Sciences

Statistics for the Social Sciences. Psychology 340 Spring 2005. Factorial ANOVA. 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

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Statistics for the Social Sciences

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  1. Statistics for the Social Sciences Psychology 340 Spring 2005 Factorial ANOVA

  2. 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

  3. 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

  4. More than two groups • Independent groups • More than one Independent variable • The factorial (between groups) ANOVA: Statistical analysis follows design

  5. 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

  6. Partitioning the variance Total variance Stage 1 Within groups variance Between groups variance Stage 2 Factor A variance Factor B variance Interaction variance

  7. Factorial ANOVA in SPSS • Go through how to set up SPSS to conduct a factorial ANOVA

  8. Effect Size in Factorial ANOVA

  9. Approximate Sample Size Needed in Each Cell for 80% Power (.05 significance level)

  10. 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.

  11. Extensions and Special Cases of the Factorial ANOVA • Three-way and higher ANOVA designs • Repeated measures ANOVA

  12. 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: • He’ll be by at the end of class today • E-mail him about your interest: jhkahn@ilstu.edu

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