
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: tlumley@u.washington.edu
> To: jinghuazhao@hotmail.com
> CC: r-devel@stat.math.ethz.ch
> 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
> tlumley@u.washington.edu	University of Washington, Seattle

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