A Source Like Any Other? Field and Survey Experiment Evidence on How Interest Groups Shape Public Opinion

One result of political polarization is that citizens often react differently to new information, depending on whether they trust the communicator. Extensive evidence documents motivated reasoning and reliance on source cues for party communication. However, even in times of polarization and high political awareness citizens do not have strong attitudes towards all kinds of actors that engage in public communication. In particular, many low-profile interest groups are hardly known to the wider public. In a new study, recently published in the Journal of Communication, we (Jungherr, Wuttke, Mader, Schoen) argue that interest group communication follows different mechanisms than party communication which has previously been the focus of scholarly attention. Because most citizens lack crystallized attitudes towards low-profile interest groups, the persuasive effect of interest group communication is more homogenous than party communication so that interest groups are in a better position to persuade citizens with any political background.  

Treatment effects on attitudes towards TTIP

One aspect I like about this study, which has been years in the making, is how the study investigates the effects of interest group communication. First, we conduct a large-scale combined field- and survey-experiment in which individuals are randomly assigned to interest group communication. We partnered up with „Arbeitgeberverband Gesamtmetall“ who at the same time was interested in the efficacy of advocating for the controversial free trade agreement TTIP. Whereas one-third of respondents received no communication, the remainder were exposed to a letter that argued for the interest group’s position on this issue. Interestingly, half of the individuals received the treatment embedded in a survey-experimental which is common practice in the social sciences and allows researchers to closely examine treatment effects in a controlled setting. Yet, the other half received the letter via postal mail without any reference to our study, allowing us the investigate the persuasive effects in a realistic setting. We saw that the interest group communication succeeded in changing minds on TTIP. For every 13 letters the interest group had sent out, one person was converted from opponent to supporter of TTIP. Notably, prior attitudes towards the interest group played no discernible role in how citizens reacted to the letter, neither in the field-experimental setting nor in the more controlled survey experiment. 

Two additional studies extend this evidence to strengthen the finding that interest group communication works independently of prior credibility assessments of the source. Study 2 presents evidence in line with our pre-registered hunch that citizens have much weaker predispositions towards interest groups compared to political parties. Study 3 then puts our idea of differential effects across types of senders to a formal test in a pre-registered, highly powered survey experiment. We exposed 8,500 survey respondents to a communicative treatment where the sender cue was randomly varied. As expected, when the communication was ostensibly from a political party, the treatments only had a persuasive effect among respondents with favorable predispositions towards that party – whereas the treatment even backfired among respondents with negative attitudes towards the party. When the communication was from an interest group, prior attitudes made no difference. 

Feel free to browse the study or use our reproduction material to build on our work and let us know if you find any errors we made in the analysis. 

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