The dependence of voter shares under a two-vote system

Abstract

In an electoral system where each voter is allowed to select up to two candidates in a double-seat constituency, the combination of votes forms a special kind of contingency table. The usual hypothesis of complete independence of the voter shares for the candidates is of interest, but it is shown to be almost unattainable. The correlation coefficient of the voter shares is constructed. It is shown to be equivalent to Pearson's phi coefficient. The limitations of the coefficient are discussed. It is found that the use of conditional probabilities gives a better understanding of the dependence of the voter shares under the system considered.