A general measure of district competitiveness

We propose a new general measure of district competitiveness that can be applied to both PR and SMP systems. We define competitiveness as the degree of uncertainty in the outcome of an election, and so the measure of competitiveness is the minimal number of additional votes required for any party to win one additional seat. We show that this corresponds to margin of victory in an SMP system and we illustrate how this can be computed in a PR system. We also argue that while it makes sense to take into account the total number of votes cast in the district it is also imperative to consider the number of seats contested. We compare district competitiveness in two SMP and two PR countries. The findings challenge the conventional wisdom that elections are more competitive and that local competitiveness is less variable under PR than under SMP. We finally show that the impact of competitiveness on turnout decreases with district magnitude.