Three programs for computing Dunn-Sidák critical values.
The Dunn-Sidák multiple comparison procedure is used to test hypotheses and construct confidence intervals for two or more a priori nonorthogonal contrasts for population means. The procedure uses a levels that are not available in conventional t tables. In 1977 Games prepared a table of two tailed critical values that simplifies using the procedure. Researchers are accustomed to doubling alpha in a two-tailed t table to obtain the critical value in one tail. Unfortunately, doubling alpha in Games's table always gives one tailed critical values that are too small. Computational routines using the t inverse function in Microsoft Excel 98, SAS, and SPSS are presented for obtaining Dunn-Sidák one- and two-tailed critical values for ant familywise error rate, number of contrasts, and error degrees of freedom.