[R] p-values < 2.2e-16 not reported

Gustaf Rydevik gustaf.rydevik at gmail.com
Wed May 19 11:10:45 CEST 2010

On Wed, May 19, 2010 at 10:53 AM, Will Eagle <will.eagle at gmx.net> wrote:
> Dear all,
> how can I get the exact p-value of a statistical test like cor.test() if the
> p-value is below the default machine epsilon value of .Machine$double.eps =
>  2.220446e-16?
> At the moment smaller p-values are reported as "p-value < 2.2e-16".
> .Machine$double.eps <- 1E-100 does not solve this issue, although this value
> should be used by the format.pval() function.
> To know the exact p-values down to 1E-200 is very important since I have
> multiple tests which require a alpha error-threshold below 2.2E-16.
> Thanks in advance,
> Will

I would be interested to hear about what kind of multiple testing
you're doing. Genetics?

Intuitively, requiring that small p-values would seem to throw away
most any interesting results that are not simply errors in your data -
are you sure that there's not a better way of thinking about your

>From a practical standpoint, I would be sceptical about the ability of
most R-algorithms to generate theoretically valid p-values of such a
small order.....

Best regards,

Gustaf Rydevik, M.Sci.
tel: +46(0)703 051 451
address:Essingetorget 40,112 66 Stockholm, SE

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