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Re: st: power calculation graphs


From   Neil Shephard <nshephard@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: power calculation graphs
Date   Fri, 20 Aug 2010 10:04:11 +0000

On Fri, Aug 20, 2010 at 8:54 AM, Nikolaos Pandis <npandis@yahoo.com> wrote:
> Hi to all.
>
> I was wondering if someone would be able to help me draw the following sample calculation graphs with Stata:
>
> 1. Two arm parallel trial, outcome binary.
>
> A power (y-axis) sample size (x-axis) calculation graph for various failure proportions between trial arms. For example, p1=0.80 and p2=0.85, or p1=0.80 p=0.90 or p1=0.80 p=0.95
>
>
> 2. Two arm parallel trial, outcome continuous.
>
> A power (y-axis) sample (x-axis) calculation graph for various failure proportions between trial arms. For example, m1= 100 and m2= 120 with equal sd1=sd2=10. It would be great if I could vary m1, m2, sd (always sd1=sd2)
>

You can do both of these using the -sampsi- command and could have
found this yourself by typing -search sample size- into Stata.

If you want to do the analysis for a range of values then you should
consider putting each call within a series of nested -forval- loops
and write the results to a file using -postfile- which you can then
read into Stata and draw the graphs you want.

I'll leave the actual coding of this as an exercise for you to work on ;-)

Neil

-- 
"One should as a rule, respect public opinion in so far as is
necessary to avoid starvation and to keep out of prison, but anything
that goes beyond this is voluntary submission to an unnecessary
tyranny, and is likely to interfere with happiness in all kinds of
ways..." - Bertrand Russell

Email - nshephard@gmail.com
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