The perm.test function in exactRankTests makes reference to the StatXact manual, so presumably that would have the exact details.  The details section of the help file refers to converting real values to integers, so I expect that it is not doing what many of us think of as a permutation test, and I would not think that it is using t-statistics.

R is powerful enough that a permutation test can be run in just a few lines of R code without needing a specialized function.  And when you do it that way, you know exactly what is being done.

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow@imail.org
801.408.8111

From: Xiang Gao [mailto:xianggao2006@gmail.com]
Sent: Friday, April 23, 2010 8:52 AM
To: Greg Snow; djmuser@gmail.com
Cc: r-help@r-project.org
Subject: Re: [R] What is the test statistics in perm.test

Thanks for all your reply.  I am a biologist and only start to use R recently. Yes, It is my fault. I assume that perm.test is a very popular method. Thanks for Dennis to point out that it is in exactRankTests package. I did not realize that there are so many R package. I guess I did not ask the right question and neither in the right way.

Based on my limited knowledge on statistics, it seems like use t-statistics to test the permutation. I am just not sure.

Xiang





exactRankTests
On Fri, Apr 23, 2010 at 9:13 AM, Greg Snow <Greg.Snow@imail.org<mailto:Greg.Snow@imail.org>> wrote:
There is no perm.test function in base R, is this from a package? Which package? What does the documentation for that function/package say?

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow@imail.org<mailto:greg.snow@imail.org>
801.408.8111

> -----Original Message-----
> From: r-help-bounces@r-project.org<mailto:r-help-bounces@r-project.org> [mailto:r-help-bounces@r-<mailto:r-help-bounces@r->
> project.org<http://project.org>] On Behalf Of Xiang Gao
> Sent: Thursday, April 22, 2010 1:43 PM
> To: r-help@r-project.org<mailto:r-help@r-project.org>
> Subject: [R] What is the test statistics in perm.test
>
> Hi,
>
> The permutation test for two samples in R is function perm.test(). I
> could
> not figure out what is the statistics it estimate and how many
> permutation
> it did in default?
>
> Thanks,
>
>       [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.



--
Xiang Gao, Ph.D.
Department of Biology
University of North Texas

	[[alternative HTML version deleted]]

