Post-hoc testing & familywise correction

This fact sheet explains the purpose of post-hoc testing following significant omnibus tests and why adjustment for multiple comparisons is necessary to control the familywise error rate. It outlines commonly used correction methods, including Bonferroni, Holm–Bonferroni, Tukey, Games–Howell, and related procedures, and provides guidance on selecting an appropriate approach based on study design, sample size, and variance structure. The document also contrasts post-hoc comparisons with planned contrasts and highlights common analytical pitfalls to support transparent and defensible statistical reporting.