Berry, William and Bradley Canon. “Explaining the Competitiveness of Gubernatorial Primaries.” Journal of Politics, 55 (May 1993): 454-71.

Political scientists have devoted considerable effort to explaining the extent of electoral division in democracies. In the American context, this interest has sparked research about the factors determining the nature of intraparty competition in the states. Two major explanations have emerged: the opposition hypothesis--which suggests that the strength of the opposition party is the principal determinant of intraparty competitiveness, with a weak opposition leading to strong competition--and the electoral structure hypothesis--which attributes the level of competition principally to the rules governing primaries. In particular, double (or runoff) primaries are held to offer greater incentives to politicians to compete than single primaries. Recent research about the factors determining the competitiveness of gubernatorial primaries has found stronger empirical support for the structure proposition than the opposition hypothesis. We reformulate these hypotheses in a model that presumes that electoral structure and opposition strength interact in influencing the level of competition in gubernatorial primaries such that the effect of structure on competition depends on the strength of the opposition party. Pooled cross-sectional time-series analysis of data from the states extending as far back as 1919 produces strong support for our model, leading to the conclusion that both electoral structure and opposition party strength influence the competitiveness of primaries. The empirical evidence also confirms the importance of incumbency, restrictions on gubernatorial succession, and party endorsements in determining competitiveness.