[R] how calculation degrees freedom
Peter Dalgaard
p.dalgaard at biostat.ku.dk
Fri Jan 27 23:08:28 CET 2006
Søren Højsgaard <Soren.Hojsgaard at agrsci.dk> writes:
> Along similar lines, I've noticed that the anova() function for lmer
> models now only reports the mean squares to go into the numerator
> but "nothing for the denominator" of an F-statistic; probably in
> recognition of the degree of freedom problem. It could be nice,
> however, if anova() produced even an approximate anova table which
> can be obtained from Wald tests. The anova function could then print
> that "these p-values are large sample ones and hence only
> approximate"...
I'm reasonably convinced by now that the relevant denominator is
always the residual variance, but it is happening via deep magic that
I don't quite understand... (and is quite counterintuitive to people
who are used to the traditional ANOVA decompositions in orthogonal
designs)
While we're on the subject: It would be desirable to have Wald tests
for specific terms rather than the "Type 1" (sorry, Bill) progressive
ANOVA table. Just like we already have in lme().
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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