A voting bloc is defined to be a group of voters who have similar
voting preferences. The cleavage of the Irish electorate into
voting blocs is of interest. Irish elections employ a “single
transferable vote” electoral system; under this system voters
rank some or all of the electoral candidates in order of
preference. These rank votes provide a rich source of preference
information from which inferences about the composition of the
electorate may be drawn. Additionally, the influence of social
factors or covariates on the electorate composition is of
A mixture of experts model is a mixture model in which the model
parameters are functions of covariates. A mixture of experts
model for rank data is developed to provide a model-based method
to cluster Irish voters into voting blocs, to examine the
influence of social factors on this clustering and to examine
the characteristic preferences of the voting blocs. The Benter
model for rank data is employed as the family of component
densities within the mixture of experts model; generalized
linear model theory is employed to model the influence of
covariates on the mixing proportions. Model fitting is achieved
via a hybrid of the EM and MM algorithms. An example of the
methodology is illustrated by examining an Irish presidential
election. The existence of voting blocs in the electorate is
established and it is determined that age and government
satisfaction levels are important factors in influencing voting
in this election.
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