Mauchley's test is used to assess what aspect in repeated measures designs?

Mauchley's test specifically assesses the assumption of sphericity in repeated measures designs. Sphericity refers to the equality of variances of the differences between all combinations of related groups. It is a crucial assumption in the context of analyses like repeated measures ANOVA. When sphericity is violated, it means that the variances of the differences between groups are not equal, which can lead to incorrect conclusions if not adjusted for.

In practical terms, Mauchley's test helps researchers determine whether to apply a correction (such as Greenhouse-Geisser or Huynh-Feldt corrections) to the degrees of freedom used in their analyses. By ensuring that the assumption of sphericity holds, researchers can trust that the results of their repeated measures analyses are valid and reliable.