[R] wilcox.exact() problem
David Croll
david.croll at gmx.ch
Wed Oct 28 12:27:45 CET 2009
Dear Achim,
let me thank you for this assurance!
>
> The sample size is too large (~4000 observations per group) to solve
> this problem exactly. The error message could maybe be improved, but
> the message is clear: This is too large to deal with.
>
> However, this is not a problem. With several thousand observations,
> standard normal approximations should work sufficiently well. And if
> you don't believe it, then you can look at approximate solutions that
> draw a sufficiently large number of permutations. Both is easily
> available when using wilcox_test() in "coin" as the startup message of
> "exactRankTests" suggests.
But in my dataset there are many, many tied ranks between group_1 and
group_2 and the other ones. I wanted to use the exact procedure because
I read the approximate solution would not give me exact p values in case
of tied ranks... Am I paranoid, or am I in search of an exactness
statistics cannot deliver?
Well, then I'll try permutation tests, and thank you again!
Kind regards,
David
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