[R] Post hoc Multiple comparison

Mikael Niva mikael.niva at ebc.uu.se
Mon Oct 14 10:34:07 CEST 2002

Dear R-listers

I'm a new R-user who needs some help with a test that I want to do. I
have done a field experiment: four treatments (cont, x, y and xy) at
three sites (A, B and C), the response is count data (0 - 15). I've done
a Poisson regression:

>glm(response~as.factor(treatment)*as.factor(site), family=quasipoisson,
offset(max.response), data=dat)

The "offset" is the maximum response for the sample, different for each
sample (8 - 34). To extract, I've used:

>drop1(dat.glm, .~., test="Chisq")

However, how do I do a post-hoc multiple comparison to see which
treatment(s) and interaction(s) are giving significant effects? I have
found the "multcomp package" with the "csimtest" but it requires the
"parameter estimates", how do I get these for all my "treatments" and

Yours sincerely

Mikael Niva
Dept. of Plant Ecology
EBC, Uppsala universitet

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