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MORE on ANOVA What is an Error Term?What is a Mixed ANOVA?What is a Three-Way ANOVA?What is a Three-Way Interaction?Why Should You Be Careful about Higher-Order ANOVAs?
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The denominator of the F-test in any ANOVA is also called the error term. In different types of ANOVA, the error term is calculated differently. The error term always contains only non- systematic variance. What is an Error Term?
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What is a Mixed ANOVA? Factorial ANOVA with at least one between- subjects factor and at least one within- subjects factor. Dividing the variance becomes more complicated. The F-tests are interpreted in the same way.
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What is Three-Way ANOVA? Factorial ANOVA with three factors. All combinations of levels of all three factors are measured. Can be between subjects, within subjects, or mixed.
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B 1 2 1 2 B 1 2 1 2 A A C 1 2
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Effects Tested in a Three-Way ANOVA Main Effect of A Main Effect of B Main Effect of C AxB Two-way Interaction AxC Two-way Interaction BxC Two-way Interaction AxBxC Three-way Interaction
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What is a Three-Way Interaction? A two-way interaction that changes depending on the level of a third factor. Example: For inpatients, the effect of the drug is greater for people getting cognitive than behavior therapy. For outpatients, the effect of the drug is greater for people getting behavior therapy.
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Drug Prozac Placebo Therapy Cog Beh Cog Beh Setting Inpatient Outpatient 20 40 2060 20 60 20 40
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Why Should You be Careful about Higher-Order ANOVAs? You must always interpret the most complex effect that is significant Results of higher-order ANOVAs become difficult to interpret “Never eat anything bigger than your head.”
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