[R] about a p-value < 2.2e-16

Spencer Graves @pencer@gr@ve@ @end|ng |rom e||ect|vede|en@e@org
Fri Mar 19 06:05:06 CET 2021

       I would push back on that from two perspectives:

             1.  I would study exactly what the journal said very 
carefully.  If they mandated "wilcox.test", that function has an 
argument called "exact".  If that's what they are asking, then using 
that argument gives the exact p-value, e.g.:

 > wilcox.test(rnorm(100), rnorm(100, 2), exact=TRUE)

         Wilcoxon rank sum exact test

data:  rnorm(100) and rnorm(100, 2)
W = 691, p-value < 2.2e-16

             2.  If that's NOT what they are asking, then I'm not 
convinced what they are asking makes sense:  There is is no such thing 
as an "exact p value" except to the extent that certain assumptions 
hold, and all models are wrong (but some are useful), as George Box 
famously said years ago.[1]  Truth only exists in mathematics, and 
that's because it's a fiction to start with ;-)

       Hope this helps.
       Spencer Graves


On 2021-3-18 11:12 PM, Bogdan Tanasa wrote:
>   <https://meta.stackexchange.com/questions/362285/about-a-p-value-2-2e-16>
> Dear all,
> i would appreciate having your advice on the following please :
> in R, the wilcox.test() provides "a p-value < 2.2e-16", when we compare
> sets of 1000 genes expression (in the genomics field).
> however, the journal asks us to provide the exact p value ...
> would it be legitimate to write : "p-value = 0" ? thanks a lot,
> -- bogdan
> 	[[alternative HTML version deleted]]
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