Question about zero-inflated Poisson glmer
Dear group - I am currently fitting a Poisson glmer where I have an excess of outcomes that are zero (>95%). I am now debating on how to proceed and came up with three options: 1.) Just fit a regular glmer to the complete data. I am not fully sure how interpret the coefficients then, are they more optimizing towards distinguishing zero and non-zero, or also capturing the differences in those outcomes that are non-zero? 2.) Leave all zeros out of the data and fit a glmer to only those outcomes that are non-zero. Then, I would only learn about differences in the non-zero outcomes though. 3.) Use a zero-inflated Poisson model. My data is quite large-scale, so I am currently playing around with the EM implementation of Bolker et al. that alternates between fitting a glmer with data that are weighted according to their zero probability, and fitting a logistic regression for the probability that a data point is zero. The method is elaborated for the OWL data in: https://groups.nceas.ucsb.edu/non-linear-modeling/projects/owls/WRITEUP/owls.pdf I am not fully sure how to interpret the results for the zero-inflated version though. Would I need to interpret the coefficients for the result of the glmer similar to as I would do for my idea of 2)? And then on top of that interpret the coefficients for the logistic regression regarding whether something is in the perfect or imperfect state? I am also not quite sure what the common approach for the zformula is here. The OWL elaborations only use zformula=z~1, so no random effect; I would use the same formula as for the glmer. I am appreciating some help and pointers. Thanks! Philipp