Presentation on theme: "Factorial Designs Passer Chapter 9"— Presentation transcript:
1 Factorial Designs Passer Chapter 9 Slides Prepared by Alison L. O’Malley
2 Factorial designs include two or more independent variables What does it mean for a design to be “crossed”?
3 Describing Factorial Designs In a between-subjects factorial design, each participant experiences only one conditionIn a within-subjects factorial design, each participant experiences every conditionMixed-factorial designs include one or more between-subjects variables and one or more within-subjects variables
4 Describing Factorial Designs “two by four by three”Order of variables can be reversed,so long as numbers match upNote how quickly the number of participantsrequired can skyrocket!Need at least three levels to examine nonlinear effects in an IV
5 Factorial Designs Establish whether variables have a main effect IV has significant effect on DV (i.e., there is an overall mean difference)Establish interaction effectEffect of IV on DV depends on level of another IV
6 Interaction Note how the effect of Factor A on the DV depends on the level of Factor B
8 Person x Situation Factorial Design At least one subject variable along with at least one manipulated situational variableUsing gender as a subject variable and room temperature as a manipulated situational variable, develop a 2 x 2 design and a 2 x 3 designHow might the conclusions we draw here differ from those based on a research design with two or more manipulated IVs?
9 More on Main Effects and Interactions Cell meansMarginal means reflect the average of cell meansfor the relevant row or column
10 More on Main Effects and Interactions Is there a main effect of number of witnesses?
11 More on Main Effects and Interactions Is there a main effect of number of witnesses?No.
12 More on Main Effects and Interactions Is there a main effect of witness-suspect relationship?
13 More on Main Effects and Interactions Is there a main effect of witness-suspect relationship?Yes.
14 More on Main Effects and Interactions Is there a number of witnesses x witness-suspect relationship interaction?
15 More on Main Effects and Interactions Is there a number of witnesses x witness-suspect relationship interaction?No. Why not?
18 Check your work. This form of interaction is a disordinal (or crossover) interaction.
19 Another ExampleThis form of interaction is an ordinalinteraction.
20 Main Effects and Interactions What does it mean for an interaction to “qualify” a main effect? Do interactions always qualify main effects? What do interactions have to do with the external validity of researchers’ findings?
21 Analyzing the ResultsANOVA is the statistical framework for factorial designsA 2 x 2 ANOVA entails three tests of statistical significanceOne test for the main effect of Factor AAnother test for the main effect of Factor BA test for the A x B interaction
22 Analyzing the ResultsIn order to make sense of interactions, researchers look at simple main effectsThe effect of one IV at a particular level of another IVFor gender, we wouldexamine three simplemain effects
23 Analyzing the ResultsIf statistically significant simple main effects emerge, simple contrasts are performed (a type of post-hoc test)E.g., Compare men’sperformance betweendifferent pairs oftemperatures
24 Analyzing the ResultsA priori theorizing can drive hypotheses about specific mean differencesTest with planned comparisonsMean differences need not be as large to bestatistically significant
25 Three IVs Four possible interactions Three two-way interactions (A x B, A x C, B x C)One three-way interaction (A x B x C)
26 Three IVs Overall, how many tests of statistical significance would there be in a 2 x 2 x 2?