Using Multimember District Elections to Estimate the Sources of the Incumbency Advantage

In this article we use a novel research design that exploits unique features of multimember districts to estimate and decompose the incumbency advantage in state legislative elections. Like some existing related studies we also use repeated observations on the same candidates to account for unobserved factors that remain constant across observations. Multimember districts have the additional feature of copartisans competing for multiple seats within the same district. This allows us to identify both the direct office-holder benefits and the incumbent quality advantage over nonincumbent candidates from the same party. We find that the overall incumbency advantage is of similar magnitude as that found in previous studies. We attribute approximately half of this advantage to incumbents' quality advantage over open-seat candidates and the remainder to direct office-holder benefits. However, we also find some evidence that direct office-holder benefits are larger in competitive districts than in safe districts and in states with relatively large legislative budgets per capita.