On Wed, 2009-01-28 at 21:21 +0100, Stephan Kolassa wrote: > Hi Adam, > > first: I really don't know much about MANOVA, so I sadly can't help you > without learning about it an Pillai's V... which I would be glad to do, > but I really don't have the time right now. Sorry! > > Second: you seem to be doing a kind of "post-hoc power analysis", "my > result isn't significant, perhaps that's due to low power? Let's look at > the power of my experiment!" My impression is that "post-hoc power > analysis" and its interpretation is, shall we say, not entirely accepted > within the statistical community, see: > > Hoenig, J. M., & Heisey, D. M. (2001, February). The abuse of power: The > pervasive fallacy of power calculations for data analysis. The American > Statistician, 55 (1), 1-6 > > And this: > http://staff.pubhealth.ku.dk/~bxc/SDC-courses/power.pdf > > However, I am sure that lots of people can discuss this more competently > than me... > > Best wishes > Stephan >
The point of the article was that doing a so-called "retrospective" power analysis leads to logical contradictions with respect to the confidence intervals and p-values from the analysis of the data. In other words, DON'T DO IT! All the information is contained in the confidence intervals which are based on the observed data - an after the fact "power analysis" cannot provide any insight - it's not data analysis. Rick B. ______________________________________________ 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.