campaign effects in theory and practice

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grant from the Institute for Social and Economic Research at Columbia University ... generally, events that happen over the course of the campaign cause voters' ...
CAMPAIGN EFFECTS IN THEORY AND PRACTICE American Politics Research, 2001 (vol. 29, pps. 419-437) CHRISTOPHER WLEZIEN University of Oxford ROBERT S. ERIKSON Columbia University

Authors’ note: An earlier version of this manuscript was presented at the Annual Meeting of the Southern Political Science Association, Atlanta, 2000. Portions of the research also were presented at the 1999 Conference on the Design of Election Studies, Houston. We thank Bruce Carroll and Jeff May for assistance with data collection and Pat Lynch, Tim Nokken, and especially Tom Holbrook for comments and suggestions. The research has been supported by a grant from the Institute for Social and Economic Research at Columbia University and forms part of a project supported by a grant from the National Science Foundation (SBR-9731308).

Abstract While scholars debate the influence of election campaigns on electoral decision-making, they agree that campaigns do have effects. That is, there is broad agreement that campaign events can cause voters’ preferences to change. This is straightforward. Empirically identifying the effects of the campaign is much less so. We simply do not have regular readings of voter preferences over the election cycle, and the readings we do have are imperfect. Clearly, then, an important question is: Can we actually detect the effects of election campaigns? This is a fundamental empirical question. It forms the subject of this essay. In the essay, we outline the primary theoretical perspectives on campaign events and their effects. We then turn to the practice of empirically identifying these effects, focusing particularly on survey error and its consequences for empirical analysis. Using selected poll data from the 2000 presidential election cycle, we illustrate how the various forms of survey error complicate the study of campaign effects. We also offer certain solutions, though these take us only part of the way. Indeed, given the available data, it appears that all we can hope to offer are fairly general conclusions about the effects of election campaigns.

Scholars debate the influence of election campaigns on voting behavior and election outcomes (see, e.g., Alvarez, 1997; Campbell, 2000; Finkel, 1993; Gelman and King, 1993; Holbrook, 1996; Johnston, et al., 1992; Lodge, Steenbergen, and Brau, 1995; Shaw, 1999a; 1999b). They nevertheless agree that campaigns do have effects. Put directly, but very generally, events that happen over the course of the campaign cause voters’ preferences to change. This is fairly straightforward. The problem is empirically identifying these effects. We simply do not have readings of voter preferences at regular (relatively short) intervals over the election cycle, and the readings we do have are imperfect. Clearly, then, an important question is: Can we actually detect the effects of election campaigns? This is a fundamental empirical question, and forms the subject of this essay. We begin with a discussion of theoretical perspectives. The Events Perspective When studying the effects of campaigns, political scientists typically focus on the effects of particular events. Most commonly, we examine the effects of very important events, such as nominating conventions and general election debates. (For fairly recent treatments, see Holbrook, 1996; Shaw, 1999a.) This focus is understandable for a number of reasons. First, we know that conventions and debates are very visible, where a large number of people watch on television and/or acquire information about them in other ways. Second, we can anticipate these events, so our interpretation of their effects is not subject to the post hoc ergo propter hoc reduction that characterizes interpretations of the seeming effects of many other campaign events. Third, there already is evidence that they matter a lot more than other events, or at least

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that they can. This is a good place to start the study of campaign effects. However, it only tells us about the effects of certain events. We know that campaigns really represent a series of many events, of which the highly visible conventions and debates are a small number. It is fair to wonder about the effects of the other events. Indeed, there is reason to think that they actually matter more, taken together. A case study of polls during the 2000 presidential election campaign is suggestive. For this analysis, we rely on the series of poll readings from Wlezien (2001). Figure 1 displays the data. It shows Gore’s percentage share of the two-party vote intention (ignoring all other candidates) in national trial-heat polls from the beginning of the year through Election Day. The observations in the figure are the daily poll-of-polls. They represent Gore’s share for all respondents aggregated by the mid-date of the reported polling period. The procedure used exactly follows Erikson and Wlezien (1999).1 It allows readings for 173 separate days during 2000, 59 of which are concentrated in the period after Labor Day. — Figure 1 about here — In the figure we can see some pattern over time and also a lot of noise. Gore clearly began the year well behind Bush and gained through the spring, where his support settled at around 47%. This held until the conventions. We then observe the predictable convention bounces, out of which Gore emerged in the lead—with about a 52% share—heading into the fall. The polls bounce around a lot during the fall, though Gore’s support appears to drop fairly continually until just before Election Day, when it rebounded sharply. The mean daily variance of the polls is a modest 8.92 percentage points throughout the year, 5.67 percentage points after Labor Day. How much of this variance is due to the conventions and debates? For this exercise, we consider convention effects to include anything that happens from

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the opening of the Republican convention through Labor Day and debate effects to include anything that happens from the day of the first debate until 3 days after the last debate.2 We also attribute all movement in the polls during these two seasons to separate daily convention and debate events. To be perfectly clear, we estimate the unique effect of each day for which we have poll readings during the two periods. Our analysis of variance thus provides very liberal estimates of their effects. The results are shown in Table 1. In the first column of the table, we can see that the daily change in the polls during the convention season is quite meaningful. Indeed, the collective impact of this daily change is statistically significant (F24,133=2.01, p