On Tue, 16 Dec 2008, Peter Dalgaard wrote:
power.prop.test (sic) is relying heavily on asymptotic normality, as do similar
formulas. It doesn't use continuity correction, but if you're working with such
small group sizes, I suspect that the correction term is the least of your
worries and that direct simulation would be better.
In fact, for tests in 2x2 tables, it is fairly straightforward and fast to
compute the entire sampling distribution explicitly, over a grid of parameter
values.
This gives the exact power (under alternatives) and the exact Type I error
(under null). You can also compare different tests and see how much the
continuity correction moves the actual Type I error rate away from the nominal
rate.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
tlum...@u.washington.edu University of Washington, Seattle
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