[R] paired t-test vs pairwise t-test
Duncan Murdoch
murdoch at stats.uwo.ca
Thu Aug 19 21:22:12 CEST 2004
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 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?
Duncan Murdoch
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