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# Re: st: power calculation graphs

 From Nikolaos Pandis To statalist@hsphsun2.harvard.edu Subject Re: st: power calculation graphs Date Fri, 20 Aug 2010 04:01:57 -0700 (PDT)

```Dear Neal and Martin,

Thank you for the postings.

I am aware of the sampsi family of commands, I just did not know how to write the do file in order to calculate all the different values from the -sampsi- to use for the graph.

Again, many thanks.

Nick

--- On Fri, 8/20/10, Neil Shephard <nshephard@gmail.com> wrote:

> From: Neil Shephard <nshephard@gmail.com>
> Subject: Re: st: power calculation graphs
> To: statalist@hsphsun2.harvard.edu
> Date: Friday, August 20, 2010, 1:04 PM
> 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
> Website - http://slack.ser.man.ac.uk/
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```