Magnitude and vote seeking

In one of the most frequently cited articles published in Electoral Studies, Carey and Shugart [Cary, J.M., Shugart, M.S. 1995. Incentives to cultivate a personal vote: a rank ordering of electoral formulas. Electoral Studies 14(4), 417–439] hypothesized that the number of copartisans faced relative to seats available had a differential effect on the incentive to cultivate a personal vote depending on whether electoral rules allowed for intra-party competition. Across a wide array of electoral systems, we show that the number of candidates fielded per party varies within districts and that the variation is not systematically related to the total number of seats available. Thus, the widespread use of magnitude as a proxy for “copartisan crowdedness” is systematically inaccurate. We argue that the observed number of copartisans faced makes clear that a ratio to capture vote seeking incentives needs a party-in-a-district denominator to accompany the party-in-a-district numerator. That denominator is the expected number of seats to be won by each party in question.