Effect of visualising and re-expressing evidence of policy effectiveness on perceived effectiveness: a population-based survey experiment

Communicating evidence that a policy is effective can increase public support although the effects are small. In the context of policies to increase healthier eating in out-of-home restaurants, we investigate two ways of presenting evidence for a policy's effectiveness: (i) visualising and (ii) re-expressing evidence into a more interpretable form. We conducted an online experiment in which participants were randomly allocated to one of five groups. We used a 2 (text only vs visualisation) × 2 (no re-expression vs re-expression) design with one control group. Participants (n = 4500) representative of the English population were recruited. The primary outcome was perceived effectiveness and the secondary outcome was public support. Evidence of effectiveness increased perceptions of effectiveness (d = 0.14, p < 0.001). There was no evidence that visualising, or re-expressing, changed perceptions of effectiveness (respectively, d = 0.02, p = 0.605; d = −0.02, p = 0.507). Policy support increased with evidence but this was not statistically significant after Bonferroni adjustment (d = 0.08, p = 0.034, α = 0.006). In conclusion, communicating evidence of policy effectiveness increased perceptions that the policy was effective. Neither visualising nor re-expressing evidence increased perceived effectiveness of policies more than merely stating in text that the policy was effective.