Chapters 8 & 9 Advanced Experimental Design

Experimental Designs Between-subject designs  Simple randomized design  Multilevel randomized design Factorial designs Within-subject designs Group 1T (24oz Pepsi)M Group 2T (No Pepsi)M R R Group 1M Group 2M R R Group 3M Group 4M R R T (No Pepsi) T (24oz Pepsi) T (12oz Pepsi) T (16oz Pepsi)

Multilevel Between-Subject Designs and Hypothesis Testing Group 1 = Group 2 = Group 3 = Group 4 What is the null hypothesis for the multilevel Pepsi study? How do we test the null hypothesis? By calculating an F-ratio - Analysis of Variance (ANOVA) If the F-ratio is significant, how do we know which groups are different from one another? There are two approaches for finding out Post hoc tests A priori tests Group 1M Group 2M R R Group 3M Group 4M R R T (No Pepsi) T (24oz Pepsi) T (12oz Pepsi) T (16oz Pepsi)

Post Hoc Tests Group 1 vs. Group 2 Group 1 vs. Group 3 Group 1 vs. Group 4 Group 2 vs. Group 3 Group 2 vs. Group 4 Group 3 vs. Group 4 * * * * p <.05 Group 1 = 70 Group 2 = 72 Group 3 = 83 Group 4 = 75

a priori Tests Group 1 vs. Group 3 Group 2 vs. Group 3 Group 1 vs. Group 4 Group 2 vs. Group 4 * * * p <.05 Group 1 = 70 Group 2 = 72 Group 3 = 83 Group 4 = 75

Factorial Designs Pepsi No Pepsi 24 oz Pepsi Morning Afternoon Time Group C Group D Group AGroup B

Effects in Factorial Designs Main effects  Treatment differences between levels of 1 IV Interaction effects  Result of combination of two IVs There are many null hypotheses in factorial designs  There are no differences in test scores due to the amount of Pepsi consumed.  There are no differences in test scores due to the time of day the test was taken.  There are no interaction effects between amount of Pepsi consumed and time of day the test was taken.

Graphing Main and Interaction Effects Mean Score No Pepsi 24oz Pepsi Row Mean Morning70 Afternoon70 Column Mean 70 No main or interaction effects

Significant Pepsi Effects Mean Score No Pepsi 24oz Pepsi Row Mean Morning Afternoon Column Mean 7090 No time or interaction effects

Significant Time Effects Mean Score No Pepsi 24oz Pepsi Row Mean Morning90 Afternoon70 Column Mean 80 No Pepsi or interaction effects

Significant Interaction Effect Mean Score No Pepsi 24oz Pepsi Row Mean Morning Afternoon Column Mean 80 No main effects

Significant Pepsi & Interaction Effect Mean Score No Pepsi 24oz Pepsi Row Mean Morning Afternoon70 Column Mean 6080

Significant Time & Interaction Effect Mean Score No Pepsi 24oz Pepsi Row Mean Morning Afternoon Column Mean 70

Significant Pepsi & Time Effects Mean Score No Pepsi 24oz Pepsi Row Mean Morning Afternoon Column Mean 6080 No interaction effect

Significant Pepsi, Time, and Interaction Effects Mean Score No Pepsi 24oz Pepsi Row Mean Morning70 Afternoon Column Mean 7080

Within-Subject Designs Important Factors in Experimental Design  Groups must be equal before treatment Use random assignment  Try to reduce within-group (error) variance Expose same subjects to each level of treatment. Example: Effect of beer on dart throwing Group 1T (4 beers)M Group 2T (No beer)M R R