I am applying a GLM (using SPSS v. 18) using negative binomial with log link structure for analyzing the effects of different predictors in crash frequency. From what I understand model form is
Y = exp (b0 + b1*x1 + … + bn*xn)
However one of the independent variables is an exposure variable, and its effect is different from other independent variables in a way that model form should be:
Y = b0*Z^b1*exp (b2*x2 + … + bn*xn), where Z is the exposure variable and x [2…n] are the other explanatory variables
My question is: how to model this using SPSS? I will be very grateful for any help!