[R] multiple comparisons/tukey kramer

hadley wickham h.wickham at gmail.com
Sat Nov 24 00:04:38 CET 2007

> However, I don't know what exactly glht does, and the help file is
> extremely terse. It offers the following options (in contrMat()):
>      contrMat(n, type=c("Dunnett", "Tukey", "Sequen", "AVE",
>                         "Changepoint", "Williams", "Marcus",
>                         "McDermott"), base = 1)
> The only reference to the source of these tests is:
>      Frank Bretz, Alan Genz and Ludwig A. Hothorn (2001), On the
>      numerical  availability of multiple comparison procedures.
>      _Biometrical Journal_, *43*(5), 645-656.
> This is a very technical paper, which as far as I can follow, is
> primarily a discussion of the numerical methods involved in
> calculating these contrasts, rather than the contrasts themselves. I
> can't decide which one is appropriate without knowing what the
> differences are. Dunnett seems pretty straightforward. Tukey, I think,
> may refer to what is referred to as the Tukey-Kramer test in other
> sources? Are any of them related to Scheffe? I have no idea. None of
> them are related to Newman-Keuls, as several archive messages make
> very clear that this is not a valid comparison to use, so R doesn't
> implement it.
> What I need is a reference to the tests implemented in glht, so I can
> decide which one is appropriate for my data. Sequen, Changepoint et
> al. may be common terms in some fields, but not in the references I'm
> working from.

Have you read the vignette:

You can also see exactly what set of contrasts are used by each type
with the contrMat function, see the help examples for more details.



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