[R] paired t-test vs pairwise t-test

Peter Dalgaard p.dalgaard at biostat.ku.dk
Thu Aug 19 22:14:38 CEST 2004

"Jack Tanner" <ihok at hotmail.com> writes:

> From: Rolf Turner <rolf at math.unb.ca>
> >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.
> Thank you, Rolf, that's helpful. So pairwise.t.test() is used for
> comparison of more than two means. I did, indeed, confuse it with
> t.test(paired=TRUE). 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.
> Thanks again for your clairvoyance.

I didn't suggest looking at the example section of the help pages
without a reason...

It should be pretty clear example(pairwise.t.test) does give output
that pretty clearly indicates that all pairwise comparisons are being

We do have a bug though: in 1.9.1 print.pairwise.htest seems to have
gone AWOL, so that the pretty-printing is not as nice as it might have
been. (And it might also be called a buglet that there's no example
with a paired t test.)

   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

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