Whoa -- wait a minute here! The poster said that "one of the regressors" had a P-value of .01," and asked if this was believable. One of how many? -- 3? 300? What about multiplicity? How was the regression model selected -- P Values are essentially meaningless when computed **after** model selection. And what does the design look like? -- is the regressor highly correlated with others?
So I would say the short answer is that the .01 P value is meaningless without further information. The longer answer is a rant on the misuse and (ir?)relevance of P values hypothesis tests, and the like in scientific work, which I will spare you all from. However, for those who may wonder about such ravings, have a look at: http://www.philosophynow.org/issue74/74pigliucci.htm Cheers, Bert Gunter Genentech Nonclinical Biostatistics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of SNN Sent: Wednesday, October 07, 2009 7:31 AM To: r-help@r-project.org Subject: Re: [R] power? Thanks Simon for the help. Simon Blomberg-4 wrote: > > The short answer is Yes. If you reject the null hypothesis based on that > p-value, then by definition you had enough power to do that. This is > because there is a precise inverse relationship between the p-value and > the "observed" power, once you fix the effect size and the sample size. > In other words, your post-hoc power analysis would be a simple > re-statement of the p-value. There is no extra information that can be > gained from such an analysis. See: > > The American Statistician, February 2001, Vol. 55, No. 1, pp 19-24 > > Don't bother with your power analysis, unless you are planning a new > experiment. > > Simon. > > On Tue, 2009-10-06 at 13:49 -0700, SNN wrote: >> Hi, >> >> I have used multiple linear regression on a data set and one if the >> regressor was significant with a p-value =0.01 >> >> I need to calculate the power for a multiple linear regression. i.e. do I >> have enough power to believe the above p-value? >> >> >> >> > > > -- > Simon Blomberg, BSc (Hons), PhD, MAppStat. > Lecturer and Consultant Statistician > School of Biological Sciences > The University of Queensland > St. Lucia Queensland 4072 > Australia > Room 320 Goddard Building (8) > T: +61 7 3365 2506 > http://www.uq.edu.au/~uqsblomb > email: S.Blomberg1_at_uq.edu.au > > Policies: > 1. I will NOT analyse your data for you. > 2. Your deadline is your problem. > > Statistics is the grammar of science - Karl Pearson > > ______________________________________________ > 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. > > -- View this message in context: http://www.nabble.com/power--tp25776305p25787766.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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. ______________________________________________ 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.
