type III effect from glm()
On 19-Feb-09 10:38:50, Simon Pickett wrote:
Hi all,
This could be naivety/stupidity on my part rather than a problem
with model output, but here goes....
I have fitted a fairly simple model
m1<-glm(count~siteall+yrs+yrs:district,family=quasipoisson,
weights=weight,data=m[x[[i]],])
I want to know if yrs (a continuous variable) has a significant
unique effect in the model, so I fit a simplified model with the
main effect ommitted...
m2<-glm(count~siteall+yrs:district,family=quasipoisson,
weights=weight,data=m[x[[i]],])
So, above, you have fitted two models: m1, m2
then compare models using anova() anova(m1,m1b,test="F")
And here you are comparing two models: m1, m1b Could this be the reason for your result?
Analysis of Deviance Table Model 1: count ~ siteall + yrs + yrs:district Model 2: count ~ siteall + yrs:district Resid. Df Resid. Dev Df Deviance F Pr(>F) 1 1936 75913 2 1936 75913 0 0 The d.f.'s are exactly the same, is this right? Can I only test the significance of a main effect when it is not in an interaction? Thanks in advance, Simon.
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