Look what happens when you use lower.tail=FALSE (see ?pt ). If that is not your problem, perhaps you can provide a short sample vector that replicates your results?
Josh On Wed, Jun 16, 2010 at 10:02 PM, Worik R <wor...@gmail.com> wrote: > More: > > When the t-stat is > 0 should I use 'pt' differently? > > I have been checking my results and (except for the example I posted) all > the inconsistencies occur when t>0 > > Worik > > On Thu, Jun 17, 2010 at 10:30 AM, Worik R <wor...@gmail.com> wrote: > >> I have two pairs of related vectors >> x1,y1 >> >> and >> >> x2,y2 >> >> I wish to do a test for differences in means of x1 and y1, ditto x2 and y2. >> >> I am getting odd results. I am not sure I am using 'pt' properly... >> >> I have not included the raw vectors as they are long. I am interested if I >> am using R properly... >> >> > c(length(x1), length(y1), length(x2), length(y2)) >> [1] 3436 1619 2677 2378 >> >> >> First where the T-stat and the DF do not give the same result as 't.test' >> when passed into 'pt' >> >> > t.1 <- t.test(x1, y1) >> > 2 * pt(t.1$statistic, t.1$parameter) >> t >> 1.353946 >> > t.1$p.value >> [1] 0.646054 >> >> I would have thought these would have been the same. Like below.... >> >> > t.2 <- t.test(x2, y2) >> > 2 * pt(t.2$statistic, t.2$parameter) >> t >> 0.8679732 >> > t.2$p.value >> [1] 0.8679732 >> >> This is what I expect. >> >> clearly I misunderstand some thing. What is it? >> >> cheers >> Worik >> > > [[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 ______________________________________________ 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.
