At 00:35 14/08/2009, micha...@unimelb.edu.au wrote:
Full_Name: Michael J. Lew Version: R version 2.9.1 (2009-06-26) OS: OS X Submission from: (NULL) (210.49.195.149)The default function power.t.test gives inaccurate values, particularly with large sig.level. There are two reasons for me to propose that power.t.test is inaccurate: 1. When sig.level approaches 1, so should the power. However, power.t.test('n'=5,'d'=1,'sig.level'=1) yields a power of 0.9430769. I've compared it to the equivalent function in the 'pwr' package, pwr.t.test, and while power.t.test gives a smooth function with respect to sig.level, it deivates systematically more and more as sig.level is increased. pwr.t.test('n'=5,'d'=1,'sig.level'=1) gives the correct power of 1.
I think you need to set strict=TRUE when your example gives a power of 1 here.
2. I've run empirical simulations and found that the power predicted by pwr.t.test is correct and so it is clear that power.t.test is inaccurate. ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Michael Dewey http://www.aghmed.fsnet.co.uk ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
