Modelling sources of ecological fallacy within a revised Brown and Payne model of voting transitions

We present a model of voting behaviour based on a version of aggregated overdispersed multinomial distributions; relative to a similar model by \citet{BP86}, our model is based on more realistic assumptions and free from certain shortcomings of the previous model. We show that, within this model, it is possible to test for certain confounding effects due to observable covariates measured at the aggregate level; such effects, if ignored, might cause substantial bias in the estimated relation between voting decisions in two close in time elections, a phenomenon known as {\em Ecological Fallacy}. An application to a referendum following an election for the major in the town of Milan, which was interpreted as a defeat for the Berlusconi gouvernment, is used as an illustration.