A Multivariate Polya Model of Brand Choice and Purchase Incidence

Abstract

In this paper we develop an integrated stochastic model of purchase timing and brand selection which incorporates the influence of marketing mix variables, seasonality and trend, and also allows for various individual choice mechanisms. Our approach rests on the assumptions of a zero-order choice process, a Poisson timing process and purchase rates following a multivariate Gamma Distribution over the population, the scale parameters of which vary according to marketing activities and time. The resulting model is a Multivariate Polya Process, and the distribution of brand choice probabilities turns out to be a Generalized Dirichlet Distribution. Thus, most currently used zero-order models can be considered to be special cases of this approach. Furthermore, we derive a number of market diagnostics which provide insights into market structure and demonstrate the model's use for marketing strategy simulation. Based on extensive testing of the underlying hypotheses we finally validate the model using empirical data and show that it fits the market in question.