Posted by B. Douglas Ward on March 26, 2001 at 16:19:20:
In Reply to: 3dWilcoxon posted by jian on March 24, 2001 at 20:14:45:
Jian:
The Wilcoxon signed-rank test is a nonparametric test for the paired comparison
of two samples. As such, it is the nonparametric counterpart of the paired
data t-test. Since the Wilcoxon test is based on ranks, it has a discrete
distribution, whereas the t-distribution is continuous.
Your input data consists of 6 datasets, but this constitutes only 3 pairs of
numbers (i.e., 3 differences). With such a small sample size, the Wilcoxon
signed-rank test does not have much statistical power for detecting a non-zero
difference in the samples. The paired t-test might do better, but again, with
only 3 pairs (i.e., 2 dof) the statistical power will be very low.
Doug Ward