Gelman, Andrew, and Gary King. 1990. Estimating Incumbency Advantage Without Bias. American Journal of Political Science 34: 1142–1164. Copy at http://j.mp/lvMrbM
Abstract:In this paper we prove theoretically and demonstrate empirically that all existing measures of incumbency advantage in the congressional elections literature are biased or inconsistent. We then provide an unbiased estimator based on a very simple linear regression model. We apply this new method to congressional elections since 1900, providing the first evidence of a positive incumbency advantage in the first half of the century.