Dear R-helpers, I'm using a GLM with poisson errors to model integer count data as a function of one non-integer covariate.
The model formula is: log(DV) ~ glm(log(IV,10),family=poisson). I'm getting a warning because the logged DV is no longer an integer. I have three questions: 1) Can I ignore the warning, or is logging the DV (resulting in non-integers) a serious violation of the Poisson error structure? 2) If the answer to #1 is "no, don't ignore it, it's serious" then can I use a quasipoisson error structure instead (does not give the same warning) and if so are there any pitfalls to using the quasipoisson model? Are there any better alternatives for count data where the counts must be logged? Or, should I just abandon logging the DV? In that case, how could I compare the fit of a Poisson model (without logging the DV) to that of a GLM with normal errors (with a logged DV). AIC would not be valid because the DVs are different, right? 3) The quasipoisson model doesn't return an AIC value. Why, and is there anything I can do to calculate AIC manually, that would allow me to compare this model to other models? Many thanks in advance for your help! Cheers, Mark ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
