The 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. We investigate whether two interventions can enhance evidence communication: i. visualisation of evidence, 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 differing in how evidence of policy effectiveness was presented. We used a 2 (text only vs visualisation) X 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 = .14, p < .001. There was no evidence that visualising, d = .02, p = .605, or re-expressing, d = -.02, p = .507, changed perceptions of effectiveness. Policy support increased with evidence, d = .08, p = .034, but this was not statistically significant after Bonferroni adjustment, α = .006. 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.