[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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