Tempus Fugit, Incumbency Stays: Measuring the Incumbency Advantage in the U.S. Senate

This article evaluates the incumbency advantage in the U.S. Senate. We argue that existing methods utilized to measure this advantage are suboptimal to gauge the concept in the Senate. After testing and highlighting the weaknesses of some of these methods, we present an alternative way to measure the incumbency advantage based on the number of electoral victories or terms spent in office. We test the impact of this new measure on candidates' reelection prospects and their vote share by analyzing senatorial elections from 1948 to 2008. We find that the share of the vote obtained by incumbents increases linearly with time spend in office.