Well, this an explanation of what is done in the paired t-test (and why the number of df is as it is). I was too lazy to write all this. It is nice that some list members are less lazy!
--- Rolf Turner <[EMAIL PROTECTED]> wrote: > > On 9/08/2007, at 2:57 PM, Moshe Olshansky wrote: > > > As Thomas Lumley noted, there exist several > versions > > of t-test. > > <snip> > > > If you use t3 <- t.test(x,y,paired=TRUE) then > equal > > sample sizes are assumed and the number of degrees > of > > freedom is 4 (5-1). > > This is seriously misleading. The assumption is > not that the sample > sizes > are equal, but rather that there is ***just one > sample***, namely > the sample of differences. > > More explicitly the assumptions are that > > x_i - y_i > > are i.i.d. Gaussian with mean mu and variance > sigma^2. > > One is trying to conduct inference about mu, of > course. > > It should also be noted that it is a crucial > assumption for the > ``non-paired'' > t-test that the two samples be ***independent*** of > each other, as > well as > being Gaussian. > > None of this is however germane to Nair's original > question; it is > clear > that he is interested in a two-independent-sample > t-test. > > cheers, > > Rolf Turner > > ###################################################################### > Attention: > This e-mail message is privileged and confidential. > If you are not the > intended recipient please delete the message and > notify the sender. > Any views or opinions presented are solely those of > the author. > > This e-mail has been scanned and cleared by > MailMarshal > www.marshalsoftware.com > ###################################################################### > ______________________________________________ R-help@stat.math.ethz.ch 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.