Repeat-buying and the Generalized Inverse Gaussian-Poisson Distribution

SUMMARY In this article the repeat-buying theory, as originally introduced by Ehrenberg, Chatfield and Goodhardt, has been extended to include, for the mixing of the average purchase levels of individual households, a wider family of distributions, of which the traditional gamma is just a special case. Examples are presented for which the Negative Binomial distribution performs poorly but for which the new model gives an adequate representation of the observed facts.