When is sphericity a concern with the within-groups model?
A) When sample size is large
B) When the repeated factor has more than two levels
C) When using a dependent t-test
D) None of the above is correct.

Question

Quizplus · Accepted Answer

Sphericity is a concern with the within-groups model when the repeated factor has more than two levels. Sphericity refers to the assumption that the variances of the differences between all possible pairs of conditions are equal. When this assumption is violated, the F-ratio obtained from an ANOVA using the within-groups model may be biased, leading to incorrect conclusions. One way to address this is by using a correction factor, such as the Greenhouse-Geisser or Huynh-Feldt correction.

When Is Sphericity a Concern with the Within-Groups Model