Which correction is often preferred over Greenhouse-Geisser due to being less conservative?

Which correction is often preferred over Greenhouse-Geisser due to being less conservative?

• A. Huynh-Feldt
• B. Bonferroni
• C. Sidak
• D. Tukey

Answer: (A)

The idea being tested is how to adjust the F tests in a repeated-measures (within-subjects) ANOVA when the sphericity assumption is violated. When sphericity holds, the usual F tests are valid, but violations inflate Type I error. Corrections like Greenhouse-Geisser and Huynh-Feldt modify the degrees of freedom of the test to compensate. Greenhouse-Geisser is quite conservative, often shrinking the degrees of freedom a lot, which makes it harder to reach significance. Huynh-Feldt, on the other hand, uses an epsilon estimate to adjust the degrees of freedom but tends to be less conservative—especially when the estimated epsilon is not too far from 1. Because it preserves more of the test’s power while still protecting against inflated Type I error, Huynh-Feldt is often preferred over Greenhouse-Geisser. Note that the other options are not corrections for sphericity. Bonferroni, Sidak, and Tukey are adjustments used for controlling familywise error or performing post hoc pairwise comparisons, not for the within-subjects sphericity issue addressed by Greenhouse-Geisser and Huynh-Feldt.

The idea being tested is how to adjust the F tests in a repeated-measures (within-subjects) ANOVA when the sphericity assumption is violated. When sphericity holds, the usual F tests are valid, but violations inflate Type I error. Corrections like Greenhouse-Geisser and Huynh-Feldt modify the degrees of freedom of the test to compensate.

Greenhouse-Geisser is quite conservative, often shrinking the degrees of freedom a lot, which makes it harder to reach significance. Huynh-Feldt, on the other hand, uses an epsilon estimate to adjust the degrees of freedom but tends to be less conservative—especially when the estimated epsilon is not too far from 1. Because it preserves more of the test’s power while still protecting against inflated Type I error, Huynh-Feldt is often preferred over Greenhouse-Geisser.

Note that the other options are not corrections for sphericity. Bonferroni, Sidak, and Tukey are adjustments used for controlling familywise error or performing post hoc pairwise comparisons, not for the within-subjects sphericity issue addressed by Greenhouse-Geisser and Huynh-Feldt.