Highlighting Consensus Among Medical Scientists Increases Public Support for Vaccines

Evidence From a Randomized Experiment

Sander L. van der Linden; Chris E. Clarke; Edward W. Maibach


BMC Public Health. 2015;15(1207) 

In This Article


Observed differences in perceived consensus between the descriptive (M = 88.61, SE = 1.11), prescriptive (M = 90.62, SE = 1.11), and combined treatment (M = 90.27, SE = 1.06) variations were negligible; we therefore collapsed them into a single "consensus" treatment group. We conducted a Multivariate Analysis of Variance (MANOVA) to test for significant differences between the treatment conditions on the dependent variables (perceived scientific agreement, belief in the autism-vaccine link, risk perception and public support). Using Wilk's criteria, we found a significant multivariate effect F(3, 202) = 5.05, p < 0.01, Wilk's λ = 0.93. Adjusted univariate comparisons revealed a significant main effect (p < 0.01) for the consensus-message (compared to the control group) on all dependent variables (Table 1).

We also estimated a mediation model to test whether the effect of the consensus-treatment messages on public support for vaccines is mediated by changes in the level of perceived scientific agreement on vaccine safety and (reduced) belief in the autism-vaccine link. The mediation model (Fig. 1) fit the data well. As expected, the model indicates that the effect of the consensus messages on public support and belief in the autism-link are fully mediated by changes in perceptions of scientific agreement. Perceived scientific agreement functions as an important "gateway" cognition by reducing belief in the autism-link (negative effect) and by increasing public support for vaccines (positive effect) both directly as well as indirectly. The indirect effect of perceived scientific agreement (B = 0.21, SE = 0.002) on public support via reduced endorsement of the autism link is substantial (approx. 38 % of the total effect is mediated). The model also reveals that belief in the autism-link (by itself) has a strong negative effect on public support for vaccines. Notably, almost half of the variation in public support (43 %) is explained by perceived scientific agreement and belief in the autism-link. Lastly, there was no significant interaction between the treatment-intervention(s) and political ideology on the dependent variables, the consensus messages shifted the views of liberals, moderates, and conservatives alike in line with the prevailing medical consensus.

Figure 1.

Perceived scientific agreement as a "gateway belief" mediation (path) model