[R] V-value in the wilcox.test resp. wilcox.exact
Torsten Hothorn
Torsten.Hothorn at rzmail.uni-erlangen.de
Tue Oct 15 16:24:25 CEST 2002
> hi,
> when performing a wilcox.test or a wilcox.exact i get results that looks
> like this:
>
> wilcox.exact(x, mu=.5)
> Exact Wilcoxon signed rank test
>
> data: x
> V = 207, p-value = 0.0006905
> alternative hypothesis: true mu is not equal to 0.5
>
>
> the way i understand the wilcox.test (or wilcox.exact) the V-value
> represents the summed up ranks of either the positive or negative
> differences, whichever sum is BIGGER.
no. wilcox.test computes the statistic along the following lines
x <- x - mu
ZEROES <- any(x == 0)
if(ZEROES)
x <- x[x != 0]
...
r <- rank(abs(x))
STATISTIC <- sum(r[x > 0])
i.e. the sum of the ranks of the absolute values of x which belong
to positive values of x.
>
> to actually look up the p-value in a table (and to quote it in a
> publication) i need the T value, which to my understanding is the summed
> up ranks of either the positive or negative differences, whichever sum
> is SMALLER.
>
wilcox.test computes the p-value for you, no need to look up tables.
Torsten
> so i guess my question is: how do i get the T-value
>
> thanks,
> jan
>
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