[S] nonparametric pairwise comparisons

sean@rough.stanford.edu
Thu, 05 Mar 1998 10:41:31 -0800


Hi folks,

I have a time series for several study sites. I'm interested
in the differences in the mean response among sites, not necessarily
among times, so I've done a Friedman's test and verified the existence
of significant differences among sites. I'd now like to do pairwise
comparisons among my sites, and I have two S-PLUS related questions in
this regard:

1. The method of which I'm aware for these pairwise comparisons is
to calculate the U-statistic for each pair of sites, substituting the
number of times at which samples were taken (i.e. blocks) for sample
size. Does anyone have an Splus function that will do this? As near
as I can tell, I can't do a Mann-Whitney in S-PLUS at all.

2. Does anyone know of a (nonparametric) method for pairwise
comparisons that takes advantage of the temporal structure of the
data-- something along the lines of a post-hoc version of the Wilcoxon
test for paired comparisons? This would avoid losing a lot of the
structure in the data.

Thanks in advance for any suggestions.

Cheers,
Sean

*************************************
Sean Connolly
Department of Biological Sciences
Stanford University
Stanford, CA 94305-5020
(650) 723-4365
*************************************
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