Hi, thanks to all for the helpful information. In fact our colleague is indeed
keen to check for the difference. More importantly, I was in too much a haste
to drop the message as I now recalled we got around in a similar way in Stata
and SAS for a more extreme case before. JH
> Date: Thu, 7 Feb 2008 13:04:58 -0800
> From: [EMAIL PROTECTED]
> To: [EMAIL PROTECTED]
> CC: [EMAIL PROTECTED]
> Subject: Re: [Rd] pnorm
>
> 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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