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RE: st: RE: sample size estimation for cox model


From   "Kieran McCaul" <Kieran.McCaul@uwa.edu.au>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: sample size estimation for cox model
Date   Wed, 16 Sep 2009 15:55:03 +0800

...

Well if the calculation is post hoc, then you already know what the hazard ratio and the number of events are and that's all you need to calculate the power.





______________________________________________
Kieran McCaul MPH PhD
WA Centre for Health & Ageing (M573)
University of Western Australia
Level 6, Ainslie House
48 Murray St
Perth 6000
Phone: (08) 9224-2701
Fax: (08) 9224 8009
email: Kieran.McCaul@uwa.edu.au
http://myprofile.cos.com/mccaul 
http://www.researcherid.com/rid/B-8751-2008
______________________________________________
If you live to be one hundred, you've got it made.
Very few people die past that age - George Burns

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of moleps islon
Sent: Wednesday, 16 September 2009 1:29 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: RE: sample size estimation for cox model

Yes, I´m trying to do a post-hoc power calculation (for what its
worth). However I´m uncertain as to the SD. The covariate is binary
and using the SD of the covariate itself yields an SD of only 0.2..

M


On Wed, Sep 16, 2009 at 1:15 AM, Kieran McCaul <Kieran.McCaul@uwa.edu.au> wrote:
> ...
>
> I haven't used stpower before but it seems to want the SD of the
> covariate.  The diagonal of variance-covariance matrix, e(V), contains
> the variance of the estimated betas, which is not the same thing.
>
> Are you doing a post-hoc power calculation?
>
>
>
> ______________________________________________
> Kieran McCaul MPH PhD
> WA Centre for Health & Ageing (M573)
> University of Western Australia
> Level 6, Ainslie House
> 48 Murray St
> Perth 6000
> Phone: (08) 9224-2701
> Fax: (08) 9224 8009
> email: Kieran.McCaul@uwa.edu.au
> http://myprofile.cos.com/mccaul
> http://www.researcherid.com/rid/B-8751-2008
> ______________________________________________
> If you live to be one hundred, you've got it made.
> Very few people die past that age - George Burns
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of moleps islon
> Sent: Wednesday, 16 September 2009 4:04 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: sample size estimation for cox model
>
> Dear listers,
> How do I determine standard deviation (sd) for survival data in a cox
> model?
>
> Is it correct to just use y=sqrt of e(V) and plug it into
>
> stpower cox, hratio(x) sd(y) ??
>
> regards,
>
> M
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