Hi, I'm not sure how to fit the model you want in lmer, but hopefully someone will have a better idea. However, if its of interest or use I've released the package MCMCglmm that fits the model you're after. By default MCMCglmm fits rand as a residual component: m1<-MCMCglmm(Seizure ~ Base + Trt*Base + Age + V4, random=~id, family="poisson", data=dat) which I believe is the model you want. HPDinterval(m1$VCV) gives CI's on the variance components (the second of which is you rand term) Hope this helps, Jarrod
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