On Thu, 7 Feb 2008, jing hua zhao wrote:
>
> I calculated a two-sided p values according to 2*(1-pnorm(8.104474)),
> which gives 4.440892e-16. However, it appears to be 5.30E-16 by a
> colleague and 5.2974E-16 from SAS. I tried to get around with mvtnorm
> package but it turns out to be using pnorm for univariate case. I should
> have missed some earlier discussions, but for the moment is there any
> short answer for a higher precision?
pnorm(8.104474,lower.tail=FALSE)*2 gives the same answer as SAS, and
pnorm(8.104474,lower.tail=FALSE,log=TRUE)/log(10)+log(2,10)
gives the (base-10) logarithm of the p-value, which is often the preferred
genetics scale. These are much more accurate.
> Somehow these days, statistical
> geneticists are infatuated with such tiny p values!
Yes, but in my experience they are at least fairly realistic about the
lack of difference between 4e-16 and 5e-16.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
[EMAIL PROTECTED] University of Washington, Seattle
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