Think about this. What is the null hypothesis? What is the alternative? What are their distributions? What is the probability that you get a value from the alternative when the null hypothesis holds and vice versa? Then think again about the relevance of your alternative hypothesis. You'll get a better understanding of power calculation by doing such exercise.
ir. Thierry Onkelinx Statisticus / Statistician Vlaamse Overheid / Government of Flanders INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE AND FOREST Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance thierry.onkel...@inbo.be Havenlaan 88 bus 73, 1000 Brussel www.inbo.be /////////////////////////////////////////////////////////////////////////////////////////// To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher The plural of anecdote is not data. ~ Roger Brinner The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. ~ John Tukey /////////////////////////////////////////////////////////////////////////////////////////// <https://www.inbo.be> Op vr 4 okt. 2019 om 14:30 schreef Witold E Wolski <wewol...@gmail.com>: > Hi, > > power.t.test works for some range of input parameters but fails otherwise. > > > power.t.test(delta = 0.5849625, sd=0.1, power=0.8, sig.level=0.05)$n > [1] 1.971668 > > power.t.test(delta = 0.5849625, sd=0.05, power=0.8, sig.level=0.05)$n > [1] 1.620328 > > power.t.test(delta = 0.5849625, sd=0.01, power=0.8, sig.level=0.05)$n > Error in uniroot(function(n) eval(p.body) - power, c(2, 1e+07), tol = > tol, : > did not succeed extending the interval endpoints for f(lower) * f(upper) > <= 0 > In addition: Warning message: > In qt(sig.level/tside, nu, lower.tail = FALSE) : NaNs produced > > I guessing that sd is very small compared with delta, hence the > problem. But what are allowed values (ratios) of delta and sd? > > Best > Witek > > > > > > > -- > Witold Eryk Wolski > > ______________________________________________ > 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. > [[alternative HTML version deleted]] ______________________________________________ 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.
