Incumbency and Short-Term Influences on Voters

Using NES surveys from 1980 through 2000, this article examines the incumbency advantage with a series of survey reports of the vote, an approach that departs from the convention of estimating the incumbent advantage with aggregate election returns. Previous work conceptualizes the incumbency advantage as a small and stable vote bonus of six to eight percentage points since about 1970, based on aggregate electoral returns. This study provides a different perspective on the incumbency advantage, considering the behavior of individual voters instead of aggregate electoral outcomes. We conceive of incumbency as an anchor that diminishes the influence of short-term tides on voters. Further, the effect of incumbency on voters is neither small nor stable, and varies systematically with short-term political tides. This analysis revisits generalizations about the value of incumbency by looking at it from the perspective of survey-databased reports of the vote.1 The goal is not to produce a more accurate or even a different estimate of the incumbency advantage. Our locus is on the impact of incumbency on voter choice under varying short-term, election-specific conditions. This formulation is different from the traditional consideration of the influence of incumbency on election outcomes (where districts are the unit of analysis). We believe that the survey data allow us to understand more clearly how short-term forces regulate the impact of incumbency, identifying patterns that will improve our general understanding of macro influences on voter choice. The interactive effect on vote choice of short-term lorces and incumbency suggests an "anchor" model of incumbency's effect on voters that in turn provides a fuller understanding of the electoral effects of incumbency. THE TRADITIONAL APPROACH TO CALCULATING THE INCUMBENT'S ADVANTAGE The two most common ways of assessing the net value of the incumbents advantage in legislative (usually congressional) races use election results.2 Both approaches share a common definition of the incumbency advantage: the vote share bonus provided by virtue of being an incumbent. They also share the unit of analysis: the district. The two approaches differ in method. One assessment contrasts the vote in adjacent elections when an incumbent is running with the vote in that district when the incumbent does not seek election. Alford and Brady's (1993) essay on the incumbent advantage illustrates this approach. They observed the difference in terms of a "sophomore surge" and a "retirement slump," sometimes averaging the "surge" and "slump" values (yielding a "slurge" estimate).3 Less straightforward estimation techniques attempt to consider confounding effects associated with the party bias of the district and inter-party differences in incumbent success. Gelman and King (1990) produced such an estimate with a model that regressed the Democratic vote on the previous Democratic vote, the party holding the seat, and the incumbency status of the district The coefficient associated with the incumbency variable in this model presumably yields a more accurate estimate of how much better incumbents can expect to do in any given election, net of other major determinants of the vote. Although substantially different approaches, the surge, slump, and slurge estimates are similar to the regression model estimates of Gelman and King (see Jacobson 2001). The slurge estimate of the incumbent advantage averaged about 7 points between 1970 and 2000, the Gelman-King technique estimated an 8.5 point advantage. Both observe an increase in the incumbents advantage since 1970 (probably first reported by Erikson 1971), some election-to-election oscillation (Gelman-King's technique finds more inter-election variation), and-although this is not completely clear-perhaps a slight decline from a high point in the middle 1980s. Garand and Gross (1984), observed an incumbent advantage and variance in that advantage over an even longer period. …