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. -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ R-help@r-project.org mailing list 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.
