Estimation of the Incumbency Effects in the US State Legislatures: A Quasi-Experimental Approach

This paper estimates the incumbency effects in the legislative elections of 45 states in the US during the period 1968-89. I improve upon the existing measures of incumbency by using a quasi-experimental research design that isolates the effect due to incumbency from other contemporaneous factors such as candidate quality. I find that incumbency bestows a significant advantage on incumbents compared with their challengers. The incumbent candidates are about 30 percentage points more likely to win the next election and win 5.3 percentage point more votes than the challengers. However, the advantage is not as large as estimated from the previous methods.