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Advanced Experimental Design

Advanced Experimental Design. Chapters 8 & 9. Between-subject designs Simple randomized design Multilevel randomized design Factorial designs Within-subject designs. Experimental Designs. R. Group 1. T (24oz Pepsi). M. R. Group 2. T (No Pepsi). M. R. Group 1. T (No Pepsi). M. R.

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Advanced Experimental Design

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  1. Advanced Experimental Design Chapters 8 & 9

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

  3. R Group 1 T (No Pepsi) M R Group 2 M T (12oz Pepsi) R Group 3 T (16oz Pepsi) M R Group 4 T (24oz Pepsi) M Multilevel Between-Subject Designs and Hypothesis Testing What is the null hypothesis for the multilevel Pepsi study? Group 1 = Group 2 = Group 3 = Group 4 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

  4. Post Hoc Tests Group 1 = 70 Group 2 = 72 Group 3 = 83 Group 4 = 75 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

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

  6. Factorial Designs Pepsi No Pepsi 24 oz Pepsi Group A Group B Group C Morning Time Group D Afternoon

  7. 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.

  8. Graphing Main and Interaction Effects No main or interaction effects

  9. Significant Pepsi Effects No time or interaction effects

  10. Significant Time Effects No Pepsi or interaction effects

  11. Significant Interaction Effect No main effects

  12. Significant Pepsi & Interaction Effect

  13. Significant Time & Interaction Effect

  14. Significant Pepsi & Time Effects No interaction effect

  15. Significant Pepsi, Time, and Interaction Effects

  16. R Group 1 T (4 beers) M R Group 2 T (No beer) M 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

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