[R] recommendation for post-hoc tests after anova

Colm Connolly colmconn at gmail.com
Thu Apr 6 18:15:45 CEST 2006

Greetings all,

I've done some ANOVAs and have found significant effects across my
groups, so now I have to do some post-hoc tests to ascertain which of
the groups is driving the significant effect. Usually one would do
something like a Newman-Keuls or Scheffe test to get at this but based
on googling and browsing through the r-help archives R doesn't support
these and they seem to be badly received by the R community generally
(for reasons related to alpha not being properly controlled, if I
understand correctly).

I found the TukeyHSD function but on reading the help page, I'm unsure
whether it's safe for me to use it since the number of subjects in my
groups is not balanced (ctrl=6, short=9, long=9). Would you reckon
that this is "mildly unbalanced" in the spirit of the help page or
that is my caution warranted?

In the absence of NK or Scheefe tests could someone recommend an
appropriate test for me to conduct in this instance? From what I've
read in Explaining Psychological Statistics, the REGWQ test seems to
be the way to go. Can R perform this test?

Thanks for your time,


Dr Colm G. Connolly
School of Psychology and Institute of Neuroscience
The Lloyd Building
University of Dublin
Trinity College, Dublin 2, Éire

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