THE INCUMBENCY ADVANTAGE IN MULTIMEMBER DISTRICTS - EVIDENCE FROM THE US STATES

Studies of the incumbency advantage in U.S. state legislative elections have usually been limited to the relatively few states that use single-member districts exclusively. In this paper we provide a method for computing the incumbency advantage in multimember districts, based on the Gelman-King (1990) estimator for single-member districts, and use it to estimate the incumbency advantage in 40 U.S. states over the period 1970-86. We find that the incumbency advantage has increased in states using multimember districts but at a substantially lower average rate than in states with single-member districts. We also find that states in which legislators have more opportunity or ability to perform casework services for their constituents are also those in which the incumbency advantage is larger.