The Power of Ideologically Concentrated Minorities

Samuel Merrill, Bernard Grofman, Thomas Brunell and William Koetzle

Journal of Theoretical Politics, 1999, vol. 11, issue 1, 57-74

Abstract: In two-party competition, it is well known that the party whose supporters/identifiers are more ideologically concentrated can pull the overall median in the direction of its party median, while the overall mean is essentially simply an average of the two party means weighted by the number of supporters/identifiers of each party. Yet the exact nature of the relationship between the overall median and the party-specific medians has never, we believe, been fully explicated. We consider three questions relevant to unidimensional two-party political competition: The first is `What factors determine the location of the overall median relative to the medians in each political party?' The second is `What are the factors that determine the location of the overall median relative to the overall mean?' The third, and potentially most interesting, is `Under what circumstances, if any, will the median of the party with fewer supporters be closer to the overall median than that of the party with a preponderance of supporters?' For party distributions which sufficiently overlap, we show analytically how (a) degree of party support, and (b) ideological cohesion of each party's supporters trade off with one another to determine the location of the overall median relative to the party medians. In general, if the smaller party is more concentrated ideologically and if the disparity in dispersion between the two parties exceeds the disparity in the number of party identifiers, then the overall median is closer to the median of the smaller party and, ceteris paribus, the smaller party can be expected to win.

Keywords: ideological concentration; median; mixture distribution; spatial model (search for similar items in EconPapers)
Date: 1999
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Persistent link: https://EconPapers.repec.org/RePEc:sae:jothpo:v:11:y:1999:i:1:p:57-74

DOI: 10.1177/0951692899011001003

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