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PermutationTest2 with Paired Samples

To: s-news@lists.biostat.wustl.edu
Subject: PermutationTest2 with Paired Samples
From: Chris Fiebrich <fiebrich@ou.edu>
Date: Fri, 7 Apr 2006 20:52:10 -0500
I'm using PermutationTest2 to compare two samples. My data is paired, so I am using the "paired=T" option. I wasn't convinced this algorithm was working the way I thought, so I did a simple test:

a<-c(1,1,1)
b<-c(10,10,10)

c<-permutationTest2(a,data2=b,statistic=mean,paired=T)

When I view c$replicates, I see lots of 0s, 9s and -9s. How can it calculate 0 for one of the replicates if it is keeping the pairs together? I would think the only permutations would be: 1-10 and 10-1 (or -9 and 9). Obviously, it's also using 10-10 and 1-1 to get the "0" replicates.

When I use paired=F, I also get replicates that include 0, 9 and -9. I understand that.

Does anyone understand how the paired=T option works?


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