[R] multiple comparisons with generalised least squares
Sandy.Adriaenssens at UGent.be
Mon Apr 11 11:50:03 CEST 2011
Dear R users,
I have used the following model:
M1 <- gls(Nblad ~ Concentration+Season + Concentration:Season, data=DDD,
weights=varIdent(form=~ 1 | Season*Concentration))
to assess the effect of Concentration and Season on nitrogen uptake by
leaves (Nblad). I accounted for the difference in variance across the factor
levels by using the varIdent function.
Then I wanted to perform multiple comparisons with the glht function of the
glht(M1,linfct = mcp(Season = "Tukey"))
However, here I got an error message "Error in terms.default(object) : no
terms component. Error in factor_contrasts(model) : no ‘model.matrix’ method
for ‘model’ found!".
Does the glht function work with a gls model? And if not, is there an other
way to perform multiple comparisons for a gls model?
I've searched this forum for an answer to this question, but I could only
found someone with the same question which remained unanswered. I hope
someone can provide an answer now!
Many thanks in advance!
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