Hello, Mauricio,

maybe pwr.t2n.test() in package pwr or/and n.ttest() in package
samplesize do what you need/want.

 Hth  --  Gerrit

---------------------------------------------------------------------
Dr. Gerrit Eichner                   Mathematical Institute, Room 212
gerrit.eich...@math.uni-giessen.de   Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
Fax: +49-(0)641-99-32109            http://www.uni-giessen.de/eichner
---------------------------------------------------------------------

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.)



______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Reply via email to