Why should it not be the same? Its the same dataset (up to scaling) you are testing on. Your effect (mean difference) will be different, but not your (standardized) t-statistic and df and therefore not your p-value. You will get the same result for the first if you simply test t.test(a,b)
hth. Ng Stanley schrieb: > Hi, > > Given the following, > > a <- rnorm(5) > b <- rnorm(5) > c <- rnorm(5) > a.1g.scale <- scale(c(a,b,c))[1:5] > b.1g.scale <- scale(c(a,b,c))[6:10] > c.1g.scale <- scale(c(a,b,c))[11:15] > a.2g.scale <- scale(c(a,b))[1:5] > b.2g.scale <- scale(c(a,b))[6:10] > c.2g.scale <- scale(c) > a.3g.scale <- scale(a) > b.3g.scale <- scale(b) > c.3g.scale <- scale(c) > > I am puzzled why the p-values are identical for t.test(a.1g.scale, > b.1g.scale), t.test(a.2g.scale, b.2g.scale), and t.test(a, b); similarly for > t.test(a.3g.scale, b.3g.scale) and t.test(b.3g.scale, c.3g.scale); similarly > for t.test(b.1g.scale, c.1g.scale) and t.test(b, c) > > >> t.test(a.1g.scale, b.1g.scale)$p.value >> > [1] 0.7462252 > >> t.test(a.2g.scale, b.2g.scale)$p.value >> > [1] 0.7462252 > >> t.test(a.3g.scale, b.3g.scale)$p.value >> > [1] 1 > >> t.test(b.1g.scale, c.1g.scale)$p.value >> > [1] 0.4995508 > >> t.test(b.2g.scale, c.2g.scale)$p.value >> > [1] 0.885622 > >> t.test(b.3g.scale, c.3g.scale)$p.value >> > [1] 1 > >> t.test(a, b)$p.value >> > [1] 0.7462252 > >> t.test(b, c)$p.value >> > [1] 0.4995508 > > [[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. > -- Eik Vettorazzi Institut für Medizinische Biometrie und Epidemiologie Universitätsklinikum Hamburg-Eppendorf Martinistr. 52 20246 Hamburg T ++49/40/42803-8243 F ++49/40/42803-7790 ______________________________________________ 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.
