Megastudies improve the impact of applied behavioural science.

Policy-makers are increasingly turning to behavioural science for insights about how to improve citizens' decisions and outcomes1. Typically, different scientists test different intervention ideas in different samples using different outcomes over different time intervals2. The lack of comparability of such individual investigations limits their potential to inform policy. Here, to address this limitation and accelerate the pace of discovery, we introduce the megastudy-a massive field experiment in which the effects of many different interventions are compared in the same population on the same objectively measured outcome for the same duration. In a megastudy targeting physical exercise among 61,293 members of an American fitness chain, 30 scientists from 15 different US universities worked in small independent teams to design a total of 54 different four-week digital programmes (or interventions) encouraging exercise. We show that 45% of these interventions significantly increased weekly gym visits by 9% to 27%; the top-performing intervention offered microrewards for returning to the gym after a missed workout. Only 8% of interventions induced behaviour change that was significant and measurable after the four-week intervention. Conditioning on the 45% of interventions that increased exercise during the intervention, we detected carry-over effects that were proportionally similar to those measured in previous research3-6. Forecasts by impartial judges failed to predict which interventions would be most effective, underscoring the value of testing many ideas at once and, therefore, the potential for megastudies to improve the evidentiary value of behavioural science.

Forgoing earned incentives to signal pure motives.

Policy makers, employers, and insurers often provide financial incentives to encourage citizens, employees, and customers to take actions that are good for them or for society (e.g., energy conservation, healthy living, safe driving). Although financial incentives are often effective at inducing good behavior, they've been shown to have self-image costs: Those who receive incentives view their actions less positively due to the perceived incompatibility between financial incentives and intrinsic motives. We test an intervention that allows organizations and individuals to resolve this tension: We use financial rewards to kick-start good behavior and then offer individuals the opportunity to give up some or all of their earned financial rewards in order to boost their self-image. Two preregistered studies-an incentivized online experiment (n = 763) on prosocial behavior and a large field experiment (n = 17,968) on exercise-provide evidence that emphasizing the intrinsic rewards of a past action leads individuals to forgo or donate earned financial rewards. Our intervention allows individuals to retroactively signal that they acted for the right reason, which we call "motivation laundering." We discuss the implications of motivation laundering for the design of incentive systems and behavioral change.

When seeking help, women and racial/ethnic minorities benefit from explicitly stating their identity.

Receiving help can make or break a career, but women and racial/ethnic minorities do not always receive the support they seek. Across two audit experiments-one with politicians and another with students-as well as an online experiment (total n = 5,145), we test whether women and racial/ethnic minorities benefit from explicitly mentioning their demographic identity in requests for help, for example, by including statements like "As a Black woman…" in their communications. We propose that when a help seeker highlights their marginalized identity, it may activate prospective helpers' motivations to avoid prejudiced reactions and increase their willingness to provide support. Here we show that when women and racial/ethnic minorities explicitly mentioned their demographic identity in help-seeking emails, politicians and students responded 24.4% (7.42 percentage points) and 79.6% (2.73 percentage points) more often, respectively. These findings suggest that deliberately mentioning identity in requests for help can improve outcomes for women and racial/ethnic minorities.