Incumbency and the Probability of Reelection in State Legislative Elections

We build on work estimating and explaining the incumbency advantage in state legislative elections. Our work makes advances in three ways. First, our model measures the effect of incumbency on the probability of reelection, rather than on candidate vote share or margin of victory. Second, we accommodate both multimember district (MMD) elections that are excluded from most previous studies and uncontested and partially contested (MMD) races. Third, we use an improved method of controlling for the underlying partisan makeup of districts. We calculate incumbency advantage using data from elections in 96 legislative chambers across 49 states in the 1992-1994 electoral cycle. We then model relative incumbency advantage across the states as a function of institutional characteristics. We find that district type, term length, and electoral formula have substantial effects on incumbent safety; incumbents in multimember post and free-for-all districts are more vulnerable than those in traditional SMDs, as are those with four-year, rather than two-year, terms Professionalization also affects incumbency safety, and salary rather than other resources best accounts for incumbency advantage.