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Guidelines for IDing Experimental Design

Guidelines for IDing Experimental Design. Complex Designs. When a “two-way” is more than spaghetti and chili!. What are they?. Simpl e versus complex designs “One-way” versus “Two-way”, etc. Types of factorial designs Completely randomized Completely within Mixed

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Guidelines for IDing Experimental Design

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  1. Guidelines for IDing Experimental Design

  2. Complex Designs When a “two-way” is more than spaghetti and chili!

  3. What are they? • Simple versus complex designs • “One-way” versus “Two-way”, etc. • Types of factorial designs • Completely randomized • Completely within • Mixed • Variable and level shorthand 2 x 2 2 x 3 2 x 2 x 3

  4. What good are they? • Advantages of complex designs • Economy • Understanding • External validity—interactions • Example: social facilitation versus evaluation apprehension

  5. Some Data

  6. Identifying Main Effects and Interactions • Interpretation • Main effects: the overall effect of one independent variable on the dependent variable. • Interactive effects: the effect of the first independent variable on the dependent variable that is contingent on a particular level of the second independent variable. • ordinal interactions • disordinal (crossover) interactions

  7. Analysis of Complex Designs • Simplest case: the 2 x 2 design • Three classes of scientific hypotheses • Main effect of treatment method: e.g., behavioral method will be more effective than the cognitive method • Main effect of presenting problem: e.g., treatment will be more effective for habit problems than learning problems • Interaction effect of treatment method x presenting problem: e.g., cognitive therapy will be more effective for learning problems, but behavioral therapy will be more effective for habit problems

  8. Interactions: Looking at the picture…

  9. Analysis: When Interaction is Present… • Evaluate evidence descriptively • Graphs (non-parallel lines) • Tables (subtraction method) • Confirm by inferential statistics: complex ANOVA • Qualifies our interpretation of the main effect

  10. Analysis: When Interaction is NOT present… • Focus is on interpreting the main effect(s) • Analytical comparisons of the marginal means and confidence intervals with planned comparisons

  11. The “many” faces of 2 x 2s:Possible Results #1 What do we have here?

  12. The “many” faces of 2 x 2s:Possible Results #2 What do we have here?

  13. The “many” faces of 2 x 2s:Possible Results #3 What do we have here?

  14. The “many” faces of 2 x 2s:Possible Results #4 What do we have here?

  15. The “many” faces of 2 x 2s:Possible Results #5 What do we have here?

  16. The “many” faces of 2 x 2s:Possible Results #6 What do we have here?

  17. The “many” faces of 2 x 2s:Possible Results #7 What do we have here?

  18. The “many” faces of 2 x 2s:Possible Results #8 What do we have here?

  19. Interpreting Interactions • Theory testing • External validity • Ceiling and floor effects • Natural groups design

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