Communicating quantitative evidence of policy effectiveness and support for the policy: Three experimental studies

Increasing the prices of products that harm health is an effective intervention for changing behaviour to improve health but public support for such interventions is generally low. The current paper investigates whether communicating evidence of a policy's effectiveness at tackling the focal problem could increase support. Across three studies we develop an infographic for communicating quantitative evidence of the effectiveness of a hypothetical tax to tackle childhood obesity. We investigate first, whether communicating evidence of effectiveness increases (a) perceived effectiveness (Studies 1,2,3) and (b) support for the policy, and second, whether any increase in perceived effectiveness mediates an increase in support (Studies 1 & 3). In all three studies (combined N = 9654) communicating evidence of effectiveness for the intervention increased perceived effectiveness. In Study 1, communicating evidence did not change support for the policy. Variations of the infographic were developed in Study 2 with one emerging as clearer and easier to comprehend. This infographic was therefore used in Study 3 in which it increased support for the tax from 45% to 49%, an effect that was mediated by perceived effectiveness. The effect sizes were small but probably meaningful at a population level. The results of these three studies suggest the potential for presenting quantitative evidence of intervention effectiveness to increase public support. Much uncertainty remains about the most effective ways of presenting this evidence, whether similar effects are achieved by presenting unquantified evidence and whether larger effects might be achieved by presenting information other than effectiveness.