# [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

[1]
https://en.wikipedia.org/wiki/All_models_are_wrong

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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