Abstract for: A Supply and Demand Model of Political Party Growth

In this paper, we extend an existing model of the growth of political party growth by including concepts suggested by current research. In the original model, party recruitment was modelled by analogy with the spread of an infection, describing the demand-led requirements of party leaders. We include a second mode of recruitment, the supply mechanism, where people join because of the popularity of the party. We model popularity using soft variables to capture the concepts of political legitimacy and the personal political benefits of party membership. The model is developed using a modular structure that helps elucidate the feedback structure between the population variables and the soft variables and enables the effects of the soft variables to be separated from their potential measures. We apply the model to two data sets to demonstrate improvements over the original model in both data fitting and the explanatory narrative