How can I do post-hoc pairwise comparisons using Stata?
Post-hoc pairwise comparisons are commonly performed after significant effects when there are three or more levels of a factor. Stata has three built-in pairwise methods (sidak, bonferroni and scheffe) in the oneway command. Although these options are easy to use, many researchers consider the methods to be too conservative for pairwise comparisons, especially when the are many levels. The Sidak method is the least conservative of the three followed, in order, by Bonferroni and Scheffe. We will demonstrate the pairwise options in oneway on a dataset looking at write by group which is a four-level predictor. tabstat write, by(group) stat(n mean sd) Summary for variables: write by categories of: group group | N mean sd ———+—————————— 1 | 24 46.45833 8.272422 2 | 11 58 7.899367 3 | 20 48.2 9.322299 4 | 145 54.05517 9.172558 ———+—————————— Total | 200 52.775 9.478586 —————————————- oneway write group, sidak bonfe
