On Thu, 2004-08-19 at 14:42, Liaw, Andy wrote: > > From: Duncan Murdoch > > > > On Thu, 19 Aug 2004 13:42:21 -0300 (ADT), Rolf Turner > > <[EMAIL PROTECTED]> wrote : > > > > > > > >You wrote: > > > > > >> What's the difference between t.test(x, y) and > > pairwise.t.test()? Is > > >> it just that the former takes two vectors, whereas the > > latter takes a > > >> vector and a factor? > > > > > > No. The pairwise.t.test() function (according to the help > > > file) does a multiplicity of t-tests, on more than two > > > samples, adjusting the p-value to compensate for the > > > multiplicity by various methods. > > > > > > IMHO the name of this function is bad, because to me it > > > suggests doing ***paired*** t-tests, which would trip up the > > > naive user, who probably wouldn't notice or would ignore the > > > "t tests with pooled SD" message in the output. As one of > > > the Ripley fortunes says ``It really is hard to anticipate > > > just how silly users can be.'' But why go out of the way to > > > give them a chance to be silly? > > > > And Jack wrote: > > > > >But the documentation, which I valiantly tried to make sense > > of BEFORE > > >asking my stupid question, is not clear enough for this > > particular idiot. > > >Might I suggest that the documentation be altered? It could > > use an example > > >(as in, real-life applied statistical problem) of when > > pairwise.t.test() > > >ought to be used, and why t.test(paired=TRUE) would be > > inappropriate in that > > >context; it could also use a reference to some published > > paper, website or > > >some such that explains the rationale and correct procedure > > for using this > > >test. > > > > I think it's unlikely that we would rename the function; it's been > > around a while with its current name so that's a bad idea. On the > > other hand, clearer documentation is always a plus: why not submit > > some? > > I guess this is sort of related to the thread on whether R is good for > non-statisticians... The help pages in R are sort of like *nix man pages. > They give the technical information about the topic, but not necessarily the > background. E.g., the man page for `chmod' does not explain file > permissions in detail: the user is expected to learn that elsewhere. > > Perhaps other stat packages do it differently? Does SPSS manuals detail > what its t-test procedure does, including which t-test(s) it does and when > it's appropriate? That might make it easier on users, but I still think the > users should learn the appropriate use of statistical procedures > elsewhere... > > Best, > Andy
Andy, I don't know about SPSS, but SAS' documentation is available online at: http://support.sas.com/91doc/docMainpage.jsp The documentation specifically for PROC TTEST is at: http://support.sas.com/91doc/getDoc/statug.hlp/ttest_index.htm and the documentation for PROC MULTTEST is at: http://support.sas.com/91doc/getDoc/statug.hlp/multtest_index.htm Of course, to go along with the standard SAS documentation, there is the line of "Books by Users", which parallels in a fashion, the increasing number of books on R, authored by members of this community. Best regards, Marc ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
