[R] Power calculation using pwr.t.test()

[Uwe Ligges]

On 24.06.2012 17:41, Jokel Meyer wrote:
> Dear R experts,
>
> I have conducted a power calculation in order to estimate the number of
> subjects needed to detect an effect size of d=0.28 (cohen's d) for a
> difference between two independent groups (alpha level should be 0.05 and
> the effect should be detected with 80% probability).
> The results from the code below indicates that I would need n=400 subjects
> (200 in each group). This is seems so incredibly high that I mistrust my
> results & wanted to ask whether I miscalculated n?
>
> library(pwr)
> pwr.t.test(d=0.28,sig.level=0.05,power=0.8,type="two.sample",alternative="two.sided")


Good luck this is an open source software where you can easily review 
the code and check if it is right. If it is not, I'd propose to send a 
patch to the package maintainer.

Best,
Uwe Ligges




> Many thanks for you help!
> Jokel
>
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>
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