I'm fitting a generalized linear model to try to understand how the abundance of a species of freshwater fish varies in response to some environmental variables. I'm using the AIC to choose between models. My main question is which family of probability distribution to use, Poisson or Gamma?
When I use Poisson, I can't get an AIC value for the null model. The message that appears is:
The summary output is this:
Call: glm(formula = Lampetra ~ 1, family = poisson(link = log), data = cont) Deviance Residuals: Min 1Q Median 3Q Max -1.3833 -1.0154 -0.3811 0.1948 2.4742 Coefficients: Estimate Std. Error z value Pr(>|z|) (Intercept) 0.08295 0.22009 0.377 0.706 (Dispersion parameter for poisson family taken to be 1) Null deviance: 22.079 on 18 degrees of freedom Residual deviance: 22.079 on 18 degrees of freedom AIC: Inf Number of Fisher Scoring iterations: 5