Hello, Mauricio,
maybe pwr.t2n.test() in package pwr or/and n.ttest() in package
samplesize do what you need/want.
Hth -- Gerrit
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Am 20.12.2016 um 00:31 schrieb David Winsemius:
On Dec 19, 2016, at 1:47 PM, Mauricio Cornejo via R-help <r-help@r-project.org>
wrote:
Is there a function similar to stats::power.t.test that can handle unequal
variances from two samples?
I noticed that stats::t.test has an argument for indicating whether or not to
treat the two sample variances as equal. Wondering why stats::power.t.test
doesn’t have that option.
Thanks,Mauricio
[[alternative HTML version deleted]]
Because R was developed by statisticians for statisticians and they assumed
those other statisticians would know how to extend its functions when needed.
But R-help is not advertised as the place to ask such questions when you don't
have the statistical skills. (You might want to look at the code of `t.test` to
see how you might construct appropriate arguments for `power.t.test` in the
situation you imagine. Seems to me it should be fairly straightforward.
`power.t.test` is built around the non-central t-distribution and solves a
uniroot problem for the missing parameter among n, delta, power, sd, and
sig.level, given the other 4 parameters.)
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