Negative binomial additive models

The generalized additive model is extended to handle negative binomial resp onses. The extension is complicated by the fact that the negative binomial distribution has two parameters and is not in the exponential family. The m ethodology is applied to data involving DNA adduct counts and smoking varia bles among ex-smokers with lung cancer. A more detailed investigation is ma de of the parametric relationship between the number of adducts and years s ince quitting while retaining a smooth relationship between adducts and the other covariates.