[R] paired t-test vs pairwise t-test
andy_liaw at merck.com
Thu Aug 19 21:42:49 CEST 2004
> From: Duncan Murdoch
> On Thu, 19 Aug 2004 13:42:21 -0300 (ADT), Rolf Turner
> <rolf at math.unb.ca> 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
> >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
> 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
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
> Duncan Murdoch
> R-help at stat.math.ethz.ch mailing list
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