User Guide

509
Nonparametric
Te s t s
Figure 34-25
Tests for Several Related Samples dialog box
E Select t
wo or more numeric test variables.
Tests for Several Related Samples Test Types
Three tests are available to compare the distributions of several related variables.
The Frie
dman test is the nonparametric equivalent of a one-sample repeated
measures design or a two-way analysis of variance with one observation per cell.
Friedman tests the null hypothesis that k related variables come from the same
populat
ion. For each case, the k variables are ranked from 1 to k. The test statistic
is based on these ranks. Kendall’s W is a normalization of the Friedman statistic.
Kendall’s W is interpretable as the coefficient of concordance, which is a measure of
agreem
ent among raters. Each case is a judge or rater and each variable is an item or
person being judged. For each variable, the sum of ranks is computed. Kendall’s
W ranges between 0 (no agreement) and 1 (complete agreement). Cochran’s Q is
ident
ical to the Friedman test but is applicable when all responses are binary. It is
an extension of the McNemar test to the k-sample situation. Cochran’s Q tests the
hypothesis that several related dichotomous variables have the same mean. The
varia
bles are measured on the same individual or on matched individuals.