Some discrete exponential dispersion models: Poisson-Tweedie and Hinde-Demétrio classes.
In this paper we investigate two classes of exponential dispersion models (EDMs) for overdispersed count data with respect to the Poisson distribution. The first is a class of Poisson mixture with positive Tweedie mixing distributions. As an approximation (in terms of unit variance function) of the first, the second is a new class of EDMs characterized by their unit variance functions of the form μ + μ, where p is a real index related to a precise model. These two classes provide some alternatives...