User Guide

372
Chapter 21

LSD. Uses t tests to perform all pairwise comparisons between group means. No
adjustment
is made to the error rate for multiple comparisons.
 Bonferroni
.
Uses t tests to perform pairwise comparisons between group means,
but controls overall error rate by setting the error rate for each test to the
experimentwise error rate divided by the total number of tests. Hence, the
observed si
gnificance level is adjusted for the fact that multiple comparisons
are being made.
 Sidak. Pairwise multiple comparison test based on a t statistic. Sidak adjusts
the significance level for multiple comparisons and provides tighter bounds
than Bonfe
rroni.
 Scheffe.
Performs simultaneous joint pairwise comparisons for all possible
pairwise combinations of means. Uses the F sampling distribution. Can be used
to examine all possible linear combinations of group means, not just pairwise
comparis
ons.
 R-E-G-W
F.
Ryan-Einot-Gabriel-Welsch multiple stepdown procedure based on an
Ftest.
 R-E-G-W Q. Ryan-Einot-Gabriel-Welsch multiple stepdown procedure based on
the Studentized range.
 S-N-K. Makes all pairwise comparisons between means using the Studentized
range dis
tribution. With equal sample sizes, it also compares pairs of means
within homogeneous subsets, using a stepwise procedure. Means are ordered
from highest to lowest, and extreme differences are tested first.
 Tukey. Uses the Studentized range statistic to make all of the pairwise comparisons
between
groups. Sets the experimentwise error rate at the error rate for the
collection for all pairwise comparisons.
 Tukey's-b. Uses the Studentized range distribution to make pairwise comparisons
between groups. The critical value is the average of the corresponding value for
the Tuke
y's honestly significant difference test and the Student-Newman-Keuls.
 Duncan
.
Makes pairwise comparisons using a stepwise order of comparisons
identical to the order used by the Student-Newman-Keuls test, but sets a
protection level for the error rate for the collection of tests, rather than an error
rate fo
r individual tests. Uses the Studentized range statistic.
 Hochb
erg's GT2.
Multiple comparison and range test that uses the Studentized
maximum modulus. Similar to Tukey's honestly significant difference test.