[R] T statistic exactRankTests package

Peter Ehlers ehlers at ucalgary.ca
Fri May 31 00:25:34 CEST 2013

On 2013-05-30 04:20, Al Zou wrote:
> I understand this might be a silly question, but I have problems
> understanding the statistic term returned in most permutation packages.
> for example:
> x<-c(8,4,6)
> y<-c(5,3,4)
>   res<-exactRankTests::perm.test(x,y,paired=TRUE)
>           1-sample Permutation Test
> data:  x and y
> T = 6, p-value = 0.25
> alternative hypothesis: true mu is not equal to 0
> attributes(res)
> $names
> [1] "statistic"   "p.value"     "pointprob"   "null.value"  "alternative"
> "method"      "data.name"
> $class
> [1] "htest"
> res$statistic
> T
> 6
> I cannot figure out what the T stands for. I understand it is "T statistic"
> but it is not the t-score.
> Can some one tell me what formula is used for the T statistic.

The formula is simple: T is the sum of the positive paired differences.
You could check Wikipedia for "permutation test". There must be plenty
of online info but I'm too lazy to check.

> In general is there some way to look for what function is used to calculate
> the statistics?

Just look at the code of perm.test.default (it's not complicated).


to see the code or get the package source and study the code.

Peter Ehlers

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