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
$Y = \exp (b_0 + b_1 x_1 + \cdots + b_n x_n)$
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:
$Y = b_0 Z^b_1 \exp (b_2 x_2 + \cdots + b_n x_n)$, where $Z$ is the exposure variable and $x\in[2\cdots n]$ are the other explanatory variables
My question is: how to model this using SPSS?