I am working in accident prediction modeling and I'm using SPSS Generalized Linear Model procedure with Negative Binomial distribution and Log Link Function.
Does anyone know the form in wich SPSS returns the dispersion parameter?
Is it the form Var(x)=mu+dispersion*mu^2
?
All i know is that the dispersion parameter is equal to 0 for a Poisson distribution, where Var(x)=mu
.
Many thanks in advance