What are a priori and post hoc comparisons used for after an overall ANOVA?

• A. Pairwise comparisons to determine if one specific mean differs from another
• B. Testing normality
• C. Estimating effect size
• D. Computing the regression coefficients

Answer: (A)

After an overall ANOVA shows that not all group means are equal, a priori and post hoc comparisons are used to pinpoint exactly which specific pairs of means differ. These are pairwise tests of mean differences across the groups, done in a way that controls the risk of finding a difference by chance when many comparisons are made. A priori comparisons test planned hypotheses about which groups should differ, while post hoc comparisons explore all remaining pairwise differences after finding a significant overall effect, with adjustments to keep the Type I error rate in check. For example, with three groups you’d examine the differences between each pair (group 1 vs group 2, group 1 vs group 3, group 2 vs group 3) using an appropriate correction method like Tukey’s HSD. This is not about testing normality, estimating overall effect size, or computing regression coefficients—those serve different purposes in analysis.