guidelines for iding experimental design levels/ participant? one independent groups design more...
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Guidelines for IDing Experimental Design
Levels/participant?
One More than one
IndependentGroups design
RepeatedMeasures design
Once: incomplete
More than once:complete
Times each level/Participant?
Yes: all possible orders
No: selected orders
Four or fewer conditions?
Anticipation problems?
Yes: block randomization
No: ABBA counterbalancing
Complex Designs
When a “two-way” is more than spaghetti and chili!
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
What good are they?
• Advantages of complex designs
• Economy
• Understanding
• External validity—interactions
• Example: social facilitation versus evaluation apprehension
Some Data
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
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
Interactions: Looking at the picture…
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
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
The “many” faces of 2 x 2s:Possible Results #1
What do we have here?
The “many” faces of 2 x 2s:Possible Results #2
What do we have here?
The “many” faces of 2 x 2s:Possible Results #3
What do we have here?
The “many” faces of 2 x 2s:Possible Results #4
What do we have here?
The “many” faces of 2 x 2s:Possible Results #5
What do we have here?
The “many” faces of 2 x 2s:Possible Results #6
What do we have here?
The “many” faces of 2 x 2s:Possible Results #7
What do we have here?
The “many” faces of 2 x 2s:Possible Results #8
What do we have here?
Interpreting Interactions
• Theory testing
• External validity
• Ceiling and floor effects
• Natural groups design