This paper introduces a conceptualization of electoral competition suited for
broad quantitative comparative studies. The conception is based on theoretical
considerations about the consequences of vote choices for the behavior of
political elites. Departing from the notion that political parties seek to
maximize votes unconditionally, it is hypothesized that electoral
considerations matter only to the extent that vote shifts significantly effect
incumbents' prospects to remain in office. Different political-institutional
factors that capture the willingness of voters to switch votes, the
institutional efficacy of vote shifts, and the insulation of government
coalitions from such shifts affect the probability of incumbents to
remain in office. The empirical validity of these claims is assessed in an
analysis of government turnover in 36 democracies since 1945. Based
on theoretical considerations, an appropriate functional specification of how
to combine these factors into a single measure is derived. Therewith,
electoral vulnerability as the probability of government turnover due to
shifts in the electorate is proposed as a measure of political competition.
The resulting measure encompasses both the behavior of political actors such
as the electorate and political parties as well as the institutional
environment political competition is embedded in. To illustrate the
theoretical and empirical utility of the concept, the article concludes with
an empirical investigation of how electoral competition affected industry
subsidization in West European countries between 1970 and 1997.
