My dependent variable (count) shows signs of overdispersion (mean 2.50, Variance 6.60), which led me to use a negative binomial model. This seems to fit better compared to the Poisson regression (lower AIC). However, few of the significant effects I found when using the Poisson regression become highly non-significant when using the negative binomial model.
Is that normal? should I stick with the Negative Binomial regardless?