Assessing the Influence of Political Parties on Public Opinion: The Challenge from Pretreatment Effects

Despite generations of research, political scientists have trouble pinpointing the influence of political parties on public opinion. Recently, scholars have made headway in exploring whether parties in fact shape policy preferences by relying on experimental designs. Yet, the evidence from this work is mixed. I argue that the typical experiment faces a design problem that likely minimizes the extent to which parties apparently matter. Because parties have policy reputations, experimental participants may already know from real-world exposure to political debate where the parties stand before they are told in the experiment—they are “pretreated.” This study investigates how real-world political context interferes with party cue stimulus in experiments. In two experiments I show that two types of “pretreatment” from outside the experiment—exposure-based and reputation-based—dramatically moderate the effects of party cues in experiments. Moreover, the politically aware participants—who are most likely to have been pretreated before entering the experiment—are the most sensitive to this interference from real-world context. Paradoxically, experimenters are most likely to find no effect of parties at the very time that their influence is strongest outside the experiment. These findings emphasize the importance of keeping real-world context in mind when designing and analyzing experiments on political communication effects and might help reconcile disparate results of previous party cue experiments.