Launch the Generalized Linear Model personality by selecting Analyze > Fit Model, entering one or more columns for Y, and selecting Generalized Linear Model from the Personality menu.
For more information about aspects of the Fit Model window that are common to all personalities, see the Model Specification topic. Information specific to the Generalized Linear Model personality is presented here.
Specifies that an overdispersion parameter should be included in the model. Overdispersion occurs when the variance of the response is greater than would be expected by the theoretical variance of the response distribution. This can arise in Poisson and binomial response models. McCullagh and Nelder (1989) state that overdispersion is not uncommon in practice.
Specifies that the Firth bias-adjusted method is used to fit the model. This maximum likelihood-based method has been shown to produce better estimates and tests than maximum likelihood-based models that do not use bias correction. In addition, bias-corrected MLEs ameliorate separation problems that tend to occur in logistic-type models. For more information about the separation problem in logistic regression, see Firth (1993) and Heinze and Schemper (2002).