On Fri, Mar 15, 2013 at 1:05 AM, robert.koellner
<robert.koellner@email.de>wrote:

>
> But now I get new error massages:
>
> Error in wilcox.test.default(measurement, mu = 0) :
>   not enough (finite) 'x' observations
>


'Not enough' here means none. You tried to do a test on a sample of size
zero.


> In addition: There were 11 warnings (use warnings() to see them)
> > warnings()
> Warning messages:
> 1: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with ties
> 2: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with zeroes
> 3: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with zeroes
> 4: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with ties
> 5: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with ties
> 6: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with ties
> 7: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with zeroes
> 8: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with zeroes
> 9: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with ties
> 10: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with ties
> 11: In wilcox.test.default(measurement, mu = 0) :
>   cannot compute exact p-value with ties
>
> What does this mean?
> OK can´t compute with zeros, but why? The test should compare the
> mediandifference to 0 and if the values are 0 it should be 1, or not?
> And what means 'cannot compute exact p-value with ties'?
>


The classical exact distribution for the Wilcoxon signed-rank test is
derived by assuming the data are from a continuous distribution, which
implies that there cannot be any ties in the differences.   If there are
ties, the function uses a Normal approximation.

     -thomas

-- 
Thomas Lumley
Professor of Biostatistics
University of Auckland

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