after much reading I decided to write because I cannot find a solution to my question.
I already did a priori contrasts before for a continuous variable with normal distribution. Now I have another variable (burrow), which is binomial, and I can do the GLM for it. But when I do the a priori contrasts, it has no result in the cases where all data are 0 (is not that there are no data, they are just all 0 in a category (treat 30-30), and I want to compare this with others that have ones).
Data sructure is like this:
>head(burrow) ##day treat sp burrow ## 3 30-30 B 0 ## 3 30-30 B 0 ## 3 15-30 B 1 ## 3 15-30 B 1 ## 3 15-30 B 1 ## 3 10-25 B 1
My model is this:
> model4B2<-glm(burrow~ treat, family=binomial(link="logit"), data=D4B)
And I did the contrast like this:
> require(multcomp) > #Test contrasts 30 vs all (there are 4 categories to compare) > k3010R1<-matrix(c(3,-1,-1,-1),1) > t3010<-glht(model4B3.2,linfct=k3010R1) > summary(t3010)
But is not working and I am sure it should work.
Could it be because my explanatory variable is cathegorical? Or is just not possible to do contrasts for binomial when you have all 0 in some cathegory?
Thank you in advance,