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Party Affiliation, Partisanship, and Political Beliefs: A Field Experiment


Partisanship is strongly correlated with attitudes and behavior, but it is unclear from this pattern whether partisan identity has a causal effect on political behavior and attitudes. We report the results of a field experiment that investigates the causal effect of party identification. Prior to the February 2008 Connecticut presidential primary, researchers sent a mailing to a random sample of unaffiliated registered voters who, in a pretreatment survey, leaned toward a political party. The mailing informed the subjects that only voters registered with a party were able to participate in the upcoming presidential primary. Subjects were surveyed again in June 2008. Comparing posttreatment survey responses to subjects’ baseline survey responses, we find that those reminded of the need to register with a party were more likely to identify with a party and showed stronger partisanship. Further, we find that the treatment group also demonstrated greater concordance than the control group between their pretreatment latent partisanship and their posttreatment reported voting behavior and intentions and evaluations of partisan figures. Thus, our treatment, which appears to have caused a strengthening of partisan identity, also appears to have caused a shift in subjects’ candidate preferences and evaluations of salient political figures. This finding is consistent with the claim that partisanship is an active force changing how citizens behave in and perceive the political world.

Corresponding author
Alan S. Gerber is Professor, Department of Political Science, Institution for Social and Policy Studies, Yale University, 77 Prospect Street, P.O. Box 208209, New Haven, CT 06520-8209 (
Gregory A. Huber is Associate Professor, Department of Political Science, Institution for Social and Policy Studies, Yale University, 77 Prospect Street, P.O. Box 208209, New Haven, CT 06520-8209 (
Ebonya Washington is Associate Professor, Department of Economics, Yale University. P.O. Box 208264, New Haven, CT 06520-8264 (
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