Over recent years, political interest groups have extended their action repertoires. In addition to elite lobbying, public communication campaigns have become an important interest group activity. We know very little about the effects of these communicative interventions on public preferences. For example, while research on partisan communication stresses that prior attitudes toward the sender (i.e. the party/politician) are decisive for the acceptance or rejection of the message, it is not clear whether prior attitudes toward the interest group has a similar effect, given that the latter are presumably less central to people. To address this research gap, we conducted a large-scale experiment with parallel survey- and field-conditions. We tested whether an information mailing sent by a German employers’ group advocating for support of the Transatlantic Trade and Investment Partnership (TTIP) could persuade the recipients. Specifically, we conducted a three-wave panel survey with members of an online panel (Wave 1: n=7,826; Wave 2: n=6,171; Wave 3: n =4,659). Participants were randomly assigned to three balanced groups. Treatment group 1 (T1) received an issue mailing by the employers’ group advocating for the controversial TTIP agreement. Treatment group 2 (T2) received the identical information as T1 in form of a survey experiment. The remaining respondents were assigned to the control group (C) and received no treatment. Respondents of all groups participated in three survey waves. Wave 1 (W1) tested their attitudes of relevance on the issue, TTIP, and the sender, the employers’ group. Wave 2 (W2) tested their issue-specific attitudes after receiving the treatment. Wave 3 (W3) again queried their issue-specific attitudes, this time to assess the treatment’s effect decay. Our study contributes to the literature by testing—we believe for the first time—the persuasive appeal of an interest group’s public communication on an issue of high public controversy under field conditions.
