Usuario R wrote: > Hello, > Thank you, but can you understand this result? first I calculate the sd > for n = 2 and then n with that sd. It should give me 2 right? > >> FC = 1.5 >> alfa = 0.01 >> power = 0.85 >> sd1 <- power.t.test( n = 2, delta = FC, sig.level = alfa, > + power = power, type = "two.sample", sd = NULL)$sd >> >> n1 <- round( power.t.test( n = NULL, delta = FC, sig.level = > alfa,power = power, type = "two.sample", sd = sd1)$n) > Error in uniroot(function(n) eval(p.body) - power, c(2, 1e+07)) : > f() values at end points not of opposite sign
The error message pretty much says it: uniroot is looking for a root between 2 and 1e7 and complains that the root is not properly bracketed. If the root is supposed to be AT 2, then this easily happens due to rounding issues. (This could have better error trapping, but you're really not expected to be planning studies with such low 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.
