Polls and Elections: Understanding Persuasion and Activation in Presidential Campaigns: The Random Walk and Mean Reversion Models
Kaplan, Noah, Park, David K., Gelman, Andrew, Presidential Studies Quarterly
For many years political scientists have argued that campaigns have minimal effects on election outcomes. When campaign-related information flows activate latent predispositions, given balanced resources, election results are largely predetermined. (1) This perspective appears to be reinforced by the finding that election outcomes can be accurately forecast well before a campaign has run its course (Campbell 2000; Fair 1978; Lewis-Beck and Rice 1992; Rosenstone 1983). However, a consensus has emerged over the past decade among political scientists that campaigns have substantive persuasion effects (Franz and Ridout 2010; Hillygus and Jackman 2003; Huber and Arceneaux 2007; Shaw 1999a, 1999b; Vavreck 2009).
Though there has been a great deal of work on campaigns' persuasion effects over the past decade, there has been relatively little on campaigns' activation effects (see Andersen, Tilley, and Heath  for an important exception, and Huber and Arceneaux  for a recent analysis of a campaign's reinforcement effect). A few of the more recent studies of campaign effects do distinguish between types of activities and their associated persuasion effects. For example, Holbrook (1996) attempts to parse the effects of presidential conventions and debates, and Shaw (1999a) distinguishes between the persuasion effect of presidential candidate TV advertising and presidential candidate visits by state. But much of the recent work on campaigns' persuasion effects often does not attempt to distinguish between persuasion effects and activation effects. For example, Franz and Ridout (2007, 467n.1) write: "We do not distinguish here between the different processes by which advertising might influence candidate preferences; that is, we do not distinguish between attitude change brought by conversion, the activation of predisposition or the reinforcement of prior preferences." In a similar manner, Hillygus and Jackman (2003) also categorize any movement toward a candidate as a manifestation of a persuasion effect.
Here we consider only presidential general election campaigns, which are characterized by long lead times, high media exposure, only two major candidates (in most states in most years), and generally clear partisan and ideological separation between the candidates. These conditions combine to increase the predictability of votes and the stability of opinions, and to minimize feedback effects arising from polling and other sources of information that can affect expectations. We would expect multicandidate elections, primaries, low-salience elections, and nonpartisan contests to show much less stability and predictability.
In a long campaign, such as a presidential election, the performance of these persuasion and activation models should depend on the time scale being considered, and it is these changes as a campaign progresses that we discuss.
This article contributes to the existing literature conceptually and empirically. We offer clean definitions of campaigns' persuasion and activation effects, which clearly distinguish between the two types of campaign effects. These definitions permit us to estimate the extent of campaigns' activation effects. To do so, we deploy a relatively straightforward but new methodology to estimate how the effects of the "fundamentals" change over the course of the campaign. Our empirical analysis estimates the magnitude of the variance in vote choice that can be ascribed to campaigns' activation effects. Finally, based upon existing theory, we argue that activation effects should vary by partisanship and political context, and we deploy our methodology to parse the relative activation effects of the 2000, 2004, and 2008 campaigns by region and partisanship. In the end, we find that the 2000, 2004, and 2008 campaigns have substantive activation effects.
In addition to our contribution to the political science literature, this article addresses a persistent confusion in the news media, where even the most sophisticated journalistic analysts tend to assume a random walk model as a matter of course (perhaps via a mistaken analogy to the efficient markets hypothesis in finance). …