Which methods are post-hoc comparison tests?

• A. Tukey and Newman-Keuls
• B. Bonferroni and Scheffé
• C. Fisher's LSD
• D. Dunnett's test

Answer: (A)

Post-hoc comparison tests are used after an ANOVA indicates a difference to determine which group means differ while controlling for the risk of false positives across multiple comparisons. Tukey's Honestly Significant Difference test and the Newman-Keuls test are classic post-hoc procedures designed for all pairwise comparisons among group means. Tukey's HSD maintains the familywise error rate across every pair, making it a conservative and reliable choice when you want to know all the differing pairs. Newman-Keuls uses a stepwise, rank-based approach that can be more powerful in some situations, but still serves as a post-hoc method for comparing multiple means.

Other options exist for multiple comparisons but are used in different contexts. Bonferroni and Scheffé are post-hoc methods that control error rates, with varying conservativeness. Fisher's LSD is more permissive and often considered less strict for multiple comparisons unless the overall F-test is significant. Dunnett's test is tailored for comparing multiple treatments against a single control rather than all possible pairs. In this all-pairs comparison context, Tukey and Newman-Keuls are the representative post-hoc tests.