[R] wilcox.test p-value = 0

[Keo Ormsby]

Hi Murat,
I am not an expert in either statistics nor R, but I can imagine that 
since the default is exact=TRUE, It numerically computes the 
probability, and it may indeed be 0. if you use wilcox.test(x, y, 
exact=FALSE) it will give you a normal aproximation, which will most 
likely be different from zero.
Hope this helps.
Keo.

Murat Tasan escribió:
> hi, folks,
>
> how have you gone about reporting a p-value from a test when the
> returned value from a test (in this case a rank-sum test) is
> numerically equal to 0 according to the machine?
>
> the next lowest value greater than zero that is distinct from zero on
> the machine is likely algorithm-dependent (the algorithm of the test
> itself), but without knowing the explicit steps of the algorithm
> implementation, it is difficult to provide any non-zero value.  i
> initially thought to look at .Machine at double.xmin, but i'm not
> comfortable with reporting p < .Machine at double.xmin, since without
> knowing the specifics of the implementation, this may not be true!
>
> to be clear, if i have data x, and i run the following line, the
> returned value is TRUE.
>
> wilcox.test(x)$p.value == 0
>
> thanks for any help on this!
>
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