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# Re: st: sample size estimation

 From ofran almossawi To statalist@hsphsun2.harvard.edu Subject Re: st: sample size estimation Date Tue, 15 May 2012 11:46:52 +0100

```Many thanks to you Nick. This is very helpful.

On 15 May 2012 11:20, Nick Cox <njcoxstata@gmail.com> wrote:
> Without more detail this is an open question.
>
> Let's trim it right down and suppose that you are interested in
> summarizing treatments by their mean effects. Then there are three
> pairwise differences between means, say A - B, B - C, A - C. You could
> work out how big a sample you need to establish the smallest of these
> three differences reliably. Then multiply up.  At a minimum you will
> need to say something about how responses are distributed.
>
> Naturally, you didn't say that you were working with means, and a
> different specification would give a different answer.
>
> Either way, the old-fashioned answer to these questions is to suppose
> that that there is a cookbook formula you can plug into. A more modern
> approach is to simulate the effects of conditions that are plausible
>
> Nick
>
> On Tue, May 15, 2012 at 11:08 AM, ofran almossawi
> <ofran.almossawi@gmail.com> wrote:
>> Hello
>> Would anyone know how to do a sample size estimation to compare the
>> effect of a treatment on three groups. I can only find information on
>> how to compare two groups.
>>
>> Regards
>> Ofran
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```