Dear List, I have two questions regarding unbalanced data and lmer and could not find any hints in archives nor in my textbooks. 1) Is there a limit to the unbalance of case numbers in cells? Or would it be no problem if cell sizes vary between 0 and 53? 2) I have data of individual fields from a number of farms which are located in a number of regions. For 2 of 8 regions there is only 1 farm, the other regions have 2 farms. Which consequences does this fact have on the random effects part of the model summary if I choose the model lm1<-lmer(y~x1+x2+...+(1|region)+(1|region:farm))? All y and x variables are field specific. An anova(lm1, lm2) comparing with lm2<-lmer(y+x1+x2+...+(1|farm)) said models did not differ significantly and AIC was about the same. So I know there is no additional explanatory power including the region term. Yet, I would like to keep the region effect in the model to separate and compare the effect size of region vs. farm. Is it valid to do so even if some of the regions are only represented by one farm? I would appreciate any thoughts on this very much. Jana B?rger Universit?t Rostock Agrar- und Umweltwissenschaftliche Fakult?t FG Phytomedizin Satower Stra?e 48 18059 Rostock Tel. 0381-498 31 71 Fax.0381-498 31 62
unbalanced data in nested lmer model
1 message · Jana Bürger