Why do parties use primaries?: Political selection versus candidate incentives

This paper contrasts empirically two possible explanations for the party decision to use primaries: desire to improve political selection (selection effect), or desire to increase political competition—and incentives—among candidates (incentive effect). Using a simple model of endogenous primaries, I show that each explanation implies a different relation between primary adoption and the strength of partisan support. I estimate this relation using the case of Latin American presidential primaries and find robust evidence that the incentive effect dominates the selection effect.