Repeated measures ANOVA (L13) Flashcards
What are the advantages of a repeated measures ANOVA?
Reduces systematic variation, therefore more sensitive to experimental effects
Less pp’s needed, therefore less time consuming
What are the disadvantages of a repeated measures ANOVA?
Pp’s more aware of fatigue and more likely to pick up on demand characteristics
What does the variance show for a repeated measures ANOVA?
Shows the persons variability over the conditions, referred to as the SSw
Shows individual differences
How do you partition the variance?
SSt is split into SSw and SSb (variance between individuals)
SSw is further split into SSm and SSr
What is the problem with assumption of independence?
Violates assumption because scores across conditions will correlate as they depend on the same pp
What is the assumption of sphericity?
That the variances in the differences between conditions is equal (replaces assumption of independence)
Need at least three conditions for this to be an issue.
If true, you can assume analysis will be accurate
How do we identify sphericity?
Find differences in scores across conditions, calculate variance
If variances are equal then assumption is met
What is Mauchley’s test?
Tests for the assumption of sphericity.
p .05 - met
What are the estimates of sphericity?
Greenhouse-geisser
Huynh-Feldt
Lower bound
How do we quantify sphericity?
1 = perfectly spherical, therefore look at estimate value and assess how close to 1 it is
How do we correct sphericity?
Multiply the df by the estimate
G-G is more conservative
H-F is more liberal
Changes the p value, therefore results can become significant/non-significant after alteration
What are the preferred post hocs for repeated measures ANOVA?
Bonferroni, Tukey LSD (doesn’t account for multiple tests) and Sidak (less strict so less error control)
