The crowd wisdom effect is a well-established phenomenon that is widely employed for predicting and estimating variables across various domains. Previous research has focused on enhancing the wisdom of crowds by improving individual estimates while maintaining some of the initial opinion diversity. However, it is theoretically possible to increase collective accuracy by largely increasing the diversity in a crowd. In this study, we propose a method that leverages the anchoring effect to extremize individual judgments and thus increase the diversity of opinions in a crowd. This is achieved by dividing the crowd into two groups, anchoring each group to either a low or high value, and aggregating all estimates. We use a mathematical model of anchoring to determine when this strategy is expected to outperform the crowd wisdom effect. Results from three experiments provide converging evidence that the proposed approach outperforms traditional methods in estimating and forecasting unknown quantities.

Scientific evidence regularly guides policy decisions1, with behavioural science increasingly part of this process2. In April 2020, an influential paper3 proposed 19 policy recommendations (claims) detailing how evidence from behavioural science could contribute to efforts to reduce impacts and end the COVID-19 pandemic. Here we assess 747 pandemic-related research articles that empirically investigated those claims. We report the scale of evidence and whether evidence supports them to indicate applicability for policymaking. Two independent teams, involving 72 reviewers, found evidence for 18 of 19 claims, with both teams finding evidence supporting 16 (89%) of those 18 claims. The strongest evidence supported claims that anticipated culture, polarization and misinformation would be associated with policy effectiveness. Claims suggesting trusted leaders and positive social norms increased adherence to behavioural interventions also had strong empirical support, as did appealing to social consensus or bipartisan agreement. Targeted language in messaging yielded mixed effects and there were no effects for highlighting individual benefits or protecting others. No available evidence existed to assess any distinct differences in effects between using the terms physical distancing and social distancing. Analysis of 463 papers containing data showed generally large samples; 418 involved human participants with a mean of 16,848 (median of 1,699). That statistical power underscored improved suitability of behavioural science research for informing policy decisions. Furthermore, by implementing a standardized approach to evidence selection and synthesis, we amplify broader implications for advancing scientific evidence in policy formulation and prioritization.