Hello all, I have been teaching myself how to use generalized linear mixed effect models in R. While I find that the message boards like this one are extremely helpful, they have a "time travel" issue. I am finding answers to my burning questions that are years old and I am having trouble determining if the issues raised in 2006 are still issues today. So I wanted to put all of the hot topics I have been reading about, and the overly simplified answers I have gleaned in one thread. I hope others may add their burning questions and the answers they use to this thread as well?? And always the hope for comments: Q1: Should I use ML or REML to compare the fixed effects in a set of nested models using likelihood-ratio testing (LRT)? A1: It is much better to use ML to compare fixed effects in your model. Q2: Should I use ML or REML to compare the random effects in a set of nested models using likelihood-ratio testing (LRT)? A2: To test the worth of random effects in your model, REML is better. HOWEVER, if using lmer with a family specification to call glmer (family = binomial or poisson) you are automatically using ML. REML is not an option for generalized linear mixed effect models using lmer. Q3: Ok, so how do I asses the value of random effects in my generalized linear mixed effect model? A3: <insert cricket sounds here> I gather that your experimental design should be the major indicator that a random term is needed in your model specification. But sometimes showing that the random effect is valuable (perhaps in a case where none of your fixed effects are worth anything) is, in itself, an interesting result. Help? Q4: So what is the hoopla about p-values for fixed effects in lmer? A4: Short answer is that p-values are now included in the current incarnation of lme4 (can't find documentation of this but I see them so they must be there right?). The long answer about why you should be hesitant to use them and more hesitant to NEED them was provided by Doug here : http://www.nabble.com/lmer%2C-p-values-and-all-that-p4476689.html ************************************ Page E. Van Meter Michigan State University Department of Zoology vanmete7 at msu.edu **http://msu.edu/~vanmete7/*
The simple burning questions about lmer and their answers
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