[R] power.t.test formula

[Peter Dalgaard]

Usuario R wrote:
> Hi,
> 
> Does anyone of you knows a reference for the formula used in power.t.test
> function? And also why it uses the Student's distribution instead of Normal.
> (I know both of them can be used but don't see whether choose one or the
> other)

It is  a straightforward first-principles calculation. The t
distribution calculation is exact for normally distributed data with the
same unknown variance in both groups. Formulas based on the normal
distribution assumes the variance to be known, which overestimates small n.



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