User Guide

388
Chapter 22
test (sometimes liberal), or Dunnett’s C (pairwise comparison test based on the
Studentized range).
Duncan’s mul
tiple range test, Student-Newman-Keuls (S-N-K), and Tukey’s b
are range tests that rank group means and compute a range value. These tests are
not used as frequently as the tests previously discussed.
The Waller-
Duncan t test uses a Bayesian approach. This range test uses the
harmonic mean of the sample size when the sample sizes are unequal.
The significance level of the Scheffé test is designed to allow all possible linear
combinatio
ns of group means to be tested, not just pairwise comparisons available in
this feature. The result is that the Scheffé test is often more conservative than other
tests, which means that a larger difference between means is required for significance.
The least si
gnificant difference (LSD) pairwise multiple comparison test is
equivalent to multiple individual t tests between all pairs of groups. The disadvantage
of this test is that no attempt is made to adjust the observed significance level for
multiple c
omparisons.
Tests displayed. Pairwise comparisons are provided for LSD, Sidak, Bonferroni,
Games and Howell, Tamhane’s T2 and T3, Dunnett’s C, and Dunnett’s T3.
Homogene
ous subsets for range tests are provided for S-N-K, Tukey’s b, Duncan,
R-E-G-W F, R-E-G-W Q, and Waller. Tukey’s honestly significant difference test,
Hochberg’s GT2, Gabriel’s test, and Scheffé’s test are both multiple comparison
tests an
d range tests.