On Sat, Aug 7, 2010 at 1:08 PM, <josef.kar...@phila.gov> wrote: > I have read the R manual and help archives, sorry but I'm still stuck. > > How would I do a t-test with an adjusted p-value? > > Suppose that I use t.test ( ) , with the function argument alternative = > "two.sided", and data such that degrees of freedom = 20. The function > calculates a t-statistic of 2.086, and p-value =0.05 > > How do I then adjust the p-value? My thought is to do > p.adjust (pt(2.086, df=20),"BH") > but that doesn't change anything (returns 0.975) > > what is the procedure? I'm sorry if there is a basic concept that I am > missing here...
These adjustments are generally designed to control a family wise or experiment wise error rate. If you only have one p-value, then the adjustment is equivalent to the unadjusted. The argument n defaults to length(p) (which is the length of the first argument). Here are some examples: > p.adjust(p = 0.975, method = "BH") [1] 0.975 > p.adjust(p = 0.975, method = "BH", n = 1) [1] 0.975 > p.adjust(p = 0.975, method = "BH", n = 5) [1] 1 HTH, Josh > > > > > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > -- Joshua Wiley Ph.D. Student, Health Psychology University of California, Los Angeles http://www.joshuawiley.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.
