How Much of the Incumbency Advantage is Due to Scare-Off?

This paper uses a regression discontinuity design to estimate the degree to which incumbents scare off challengers with previous officeholder experience. The estimates indicate a surprisingly small amount of scare-off, at least in cases where the previous election was nearly tied. As Lee and others have shown (and as we confirm for our samples) the estimated party incumbency advantage in these same cases is quite large-in fact, it is about as large as the average incumbency advantage for all races found using other approaches. Drawing from previous estimates of the electoral value of officeholder experience, we thus calculate that scare-off in these cases accounts for only about 5-7 percent of the party incumbency advantage. We show that these patterns are similar in elections for US House seats, statewide offices and US senate seats, and state legislative seats.