variance structure
On 11-04-05 06:30 PM, Cristina Gomes wrote:
Hello, I'm running a model where the response is normally distributed and has an excess of zeros. Because I was familiar with the lmer package I used it to run a GLMM on this response, and addressed the problem of the excess of zeros by running two models: one with the response as a binary one, using the complete data set, and another excluding all the zeros and using the remaining response values in a Gaussian model. This seemed to work fine. However, a reviewer suggested using the whole data set and a zero-inflated poisson error structure in the MCMCglmm package. I don???t know if this is appropriate as my response are rates (grams of meat consumed per hr of observation) and not discrete values.
I would give advice on how to get zero-inflated models working with MCMCglmm (mainly, see Ch 5 of the "CourseNotes" vignette that comes with MCMCglmm, but I think the reviewer is wrong to think that you could use a zero-inflated Poisson. I think the way you did it is fine. However, if you *wanted* to be fancy you might (after careful reading of Ch 5, and thought) be able to set up a zero-inflated normal model in MCMCglmm in a way analogous to the way zero-inflated Poissons are set up. Ben Bolker