R help - Apr 2009 - power.t.test formula

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)

Thank you.
Regards

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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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