On Thu, 13 Mar 2003, [iso-8859-1] Cook Jane wrote:
> I've just joined up with a project that's already been going,
> and am trying to duplicate a sample size calculation. The original
> proportion of the population with a characteristic is 50%, and we
> want to detect a 10% increase with 80% power at the 5% level of
> significance. I'm told we'd need 407 patients, but can't get this
> number myself. Could someone point me to a formula or reference for
> sample size calculations.
Assuming that you are comparing 2 groups of patients on different
treatments, my estimate (via Stata) is 408 per arm, or 816 in all.
I hope that doesn't completely destroy your budget.
Paul Seed
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