Candidacy Eligibility Criteria and Party Unity

Extant research suggests that candidate selection methods can be consequential for party unity in legislative voting. Yet thus far, only variations in the selectorate and the degree of centralization have been examined. This paper argues that Candidacy Eligibility Criteria (CEC), too, have implications for party unity. I theorize that with stricter formal requirements, parties avoid adverse selection and ensure the nomination of committed candidates. By using roll-call vote data from 16 industrial democracies, candidate surveys and an original dataset consisting of nearly 500 historical party constitutions, I show that parties demanding prior membership and nudging aspirants to maintain networks within the party tend to be more unified in parliamentary voting. Moreover, their candidates, too, express greater loyalty when compared with parties without formal CEC. Thus, this paper contributes to the literatures on party unity and on candidate selection by showing how certain party rules, hitherto neglected, affect party unity.