WHY DID THE INCUMBENCY ADVANTAGE IN US HOUSE ELECTIONS GROW

Theory: A simple rational entry argument suggests that the value of in cumbency consists not just of a direct effect, reflecting the value of resources (such as staff) attached to legislative office, but also of an indirect effect, reflecting the fact that stronger challengers are less likely to contest incumbent-held seats. The indirect effect is t he product of a scare-off effect-the ability of incumbents to scare of f high-quality challengers-and a quality effect-reflecting how much el ectoral advantage a party accrues when it has an experienced rather th an an inexperienced candidate. Hypothesis: The growth of the overall i ncumbency advantage was driven principally by increases in the quality effect. Methods: We use a simple two-equation model, estimated by ord inary least-squares regression, to analyze U.S. House election data fr om 1948 to 1990. Results: Most of the increase in the incumbency advan tage, at least down to 1980, came through increases in the quality eff ect (i.e., the advantage to the incumbent party of having a low-qualit y challenger). This suggests that the task for those wishing to explai n the growth in the vote-denominated incumbency advantage is to explai n why the quality effect grew. It also suggests that resource-based ex planations of the growth in the incumbency advantage cannot provide a full explanation.