Influences of study design on the effectiveness of consensus messaging: The case of medicinal cannabis

This study examines to what extent study design decisions influence the perceived efficacy of consensus messaging, using medicinal cannabis as the context. We find that researchers' decisions about study design matter. A modified Solomon Group Design was used in which participants were either assigned to a group that had a pretest (within-subjects design) or a posttest only group (between-subjects design). Furthermore, participants were exposed to one of three messages-one of two consensus messages or a control message-attributed to the National Academies of Sciences, Engineering and Medicine. A consensus message describing a percent (97%) of agreeing scientists was more effective at shifting public attitudes than a consensus message citing substantial evidence, but this was only true in the between-subject comparisons. Participants tested before and after exposure to a message demonstrated pre-sensitization effects that undermined the goals of the messages. Our results identify these nuances to the effectiveness of scientific consensus messaging, while serving to reinforce the importance of study design.