Thanks Roger!
Kazi
----- Original Message -----
From: "Roger Newson" <[email protected]>
To: <[email protected]>
Sent: Thursday, January 06, 2005 8:32 PM
Subject: Re: st: sample size
> >Kazi Mizanur Rahman wrote:
> >
> >The baseline proportion of a an event was 0.9.
> >We assume that after providing an intervention in one group for a
particular
> >time period we get the proportion as 0.5. We also have a comparison group
> >that receives no intervention. After that particular time period the
> >proportion becomes 0.8 in the comparison group. How to calculate the
sample
> >size with 80% power and alpha .05 ?
> >
>
>---------------------------------------------------------------------------
-----
>
> Another possibility is to use the -powercal- package, downloadable from
> SSC, which can be used to do power calculations for all generalized linear
> models, including the logistic. Information on the methods and formulas
> used to do this can be found in Newson (2004). If Kazi does not have
access
> to the latest Stata Journal in a hurry, then a draft of this can be
> downloaded in preprint form from my website at
>
> http://www.kcl-phs.org.uk/rogernewson/
>
> either by using a browser or by typing in Stata
>
> findit powergen
>
> and downloading the PDF as an ancillary file. (In the longer run, of
> course, Kazi might like to subscribe to The Stata Journal, in which a lot
> of other useful things can be found.)
>
> I hope this helps.
>
> Roger
>
>
> References
>
> Newson R. Generalized power calculations for generalized linear models and
> more. The Stata Journal 2004; 4(4): 379-401.
>
>
> --
> Roger Newson
> Lecturer in Medical Statistics
> Department of Public Health Sciences
> King's College London
> 5th Floor, Capital House
> 42 Weston Street
> London SE1 3QD
> United Kingdom
>
> Tel: 020 7848 6648 International +44 20 7848 6648
> Fax: 020 7848 6620 International +44 20 7848 6620
> or 020 7848 6605 International +44 20 7848 6605
> Email: [email protected]
> Website: http://phs.kcl.ac.uk/rogernewson/
>
> Opinions expressed are those of the author, not the institution.
>
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