Identifying influential people within a community to involve in a program is an important strategy of behavioral interventions. How to efficiently identify the most effective individuals is an outstanding question. This paper compares two common strategies: consulting ‘network insiders’ versus ‘network observers’ who have knowledge of but who do not directly participate in the community. Compared to aggregating information from all insiders, asking relatively fewer observers is more cost-effective, but may come at a cost of accuracy. We use data from a large-scale field experiment demonstrating that central students, identified through the aggregated nominations of students (insiders), reduced peer conflict in 56 middle schools. Teachers (observers) also identified students they saw as influential. We compare the causal effect of the two types of nominated students on peer outcomes and the differences between the two types of students. In contrast to the prosocial effects of central students on peer conflict, teacher nominees have no, or even antisocial, influence on their peers’ behaviors. Teachers (observers) generally nominated students with traits salient to them, suggesting that observer roles may systematically bias their perception. We discuss strategies for improving observers’ ability to identify influential individuals in a network as leverage for behavioral change.

Widespread testing is key to controlling the spread of COVID-19. But should we worry about self-selection bias in the testing? The recent literature on willful ignorance says we should – people often avoid health information. In the context of COVID-19, such willful ignorance can bias testing data. Furthermore, willful ignorance often arises when selfish wants conflict with social benefits, which might be particularly likely for potential ‘super-spreaders’ – people with many social interactions – given people who test positive are urged to self-isolate for two weeks. We design a survey in which participants (n = 897) choose whether to take a costless COVID-19 test. We find that 70% would take a test. Surprisingly, the people most likely to widely spread COVID-19 – the extraverts, others who meet more people in their daily lives and younger people – are the most willing to take a test. People's ability to financially or emotionally sustain self-isolation does not matter to their decision. We conclude that people are selfless in their decision to test for COVID-19. Our results are encouraging – they imply that COVOD-19 testing may succeed in targeting those who generate the largest social benefits from self-isolation if infected, which strengthens the case for widespread testing.

We examine the causes and policy implications of strategic (willful) ignorance of risk as an excuse to over-engage in risky health behavior. In an experiment on Copenhagen adults, we allow subjects to choose whether to learn the calorie content of a meal before consuming it and then measure their subsequent calorie intake. Consistent with previous studies, we find strong evidence of strategic ignorance: 46% of subjects choose to ignore calorie information, and these subjects subsequently consume more calories on average than they would have had they been informed. While previous studies have focused on self-control as the motivating factor for strategic ignorance of calorie information, we find that ignorance in our study is instead motivated by optimal expectations – subjects choose ignorance so that they can downplay the probability of their preferred meal being high-calorie. We discuss how the motivation matters to policy. Further, we find that the prevalence of strategic ignorance largely negates the effects of calorie information provision: on average, subjects who have the option to ignore calorie information consume the same number of calories as subjects who are provided no information.

Nudges are increasingly being proposed and used as a policy tool around the world. The success of nudges depends on public acceptance. However, several questions about what makes a nudge acceptable remain unanswered. In this paper, we examine whether policy alternatives to nudges influence the public's acceptance of these nudges: Do attitudes change when the nudge is presented alongside either a more paternalistic policy alternative (legislation) or a less paternalistic alternative (no behavioral intervention)? In two separate samples drawn from the Swedish general public, we find a very small effect of alternatives on the acceptability of various default nudges overall. Surprisingly, we find that when the alternative to the nudge is legislation, acceptance decreases and perceived intrusiveness increases (relative to conditions where the alternative is no regulation). An implication of this finding is that acceptance of nudges may not always automatically increase when nudges are explicitly compared to more paternalistic alternatives.

Evidence on the effectiveness of health promotion interventions is mixed, especially in terms of the magnitude of their impact and long-term adherence. This paper proposes a comprehensive approach informed by behavioural economics of developing behavioural change programmes, which is designed to educate, activate, engage and empower people by taking into consideration individual and social mechanisms. Three applied pilots and their results are presented in order to illustrate the approach using cognitive and social mechanisms to lead to better health outcomes, individually and community-wide. More research is needed to explore levers and barriers for the systemic adoption of this framework in implementing health promotion interventions.

We report two studies investigating whether, and if so how, different low-cost interventions affect voter registration rates. Low-cost message-based interventions are increasingly used to promote target behaviours. While growing evidence shows that such ‘nudges’ often significantly impact behaviour, understanding of why interventions work or fail in particular contexts remains underdeveloped. In a natural field experiment conducted before the 2015 UK general election, we varied messages on a postcard sent by Oxford City Council to unregistered students encouraging them to join the electoral register. Our primary finding from the field study is that just one of our interventions – a reminder that people failing to register may be fined – has a significant positive impact. Offering small monetary rewards to register instead has a negative but insignificant effect. In a second study, using an online experiment we identify a particular mechanism explaining the influence of this intervention. Specifically, we show that our interventions have divergent effects on perceptions of the normative appropriateness of registering: emphasising that failing to register is punishable by law strengthened the perception that one ought to register, while offering monetary inducements for registering weakened the perception that doing so is an action already expected within society.

When people make decisions with a pre-selected choice option – a ‘default’ – they are more likely to select that option. Because defaults are easy to implement, they constitute one of the most widely employed tools in the choice architecture toolbox. However, to decide when defaults should be used instead of other choice architecture tools, policy-makers must know how effective defaults are and when and why their effectiveness varies. To answer these questions, we conduct a literature search and meta-analysis of the 58 default studies (pooled n = 73,675) that fit our criteria. While our analysis reveals a considerable influence of defaults (d = 0.68, 95% confidence interval = 0.53–0.83), we also discover substantial variation: the majority of default studies find positive effects, but several do not find a significant effect, and two even demonstrate negative effects. To explain this variability, we draw on existing theoretical frameworks to examine the drivers of disparity in effectiveness. Our analysis reveals two factors that partially account for the variability in defaults’ effectiveness. First, we find that defaults in consumer domains are more effective and in environmental domains are less effective. Second, we find that defaults are more effective when they operate through endorsement (defaults that are seen as conveying what the choice architect thinks the decision-maker should do) or endowment (defaults that are seen as reflecting the status quo). We end with a discussion of possible directions for a future research program on defaults, including potential additional moderators, and implications for policy-makers interested in the implementation and evaluation of defaults.

Do differences in worldview ideology hinder people from objectively interpreting the effect of immigration? In an experiment with Swedish adults (n = 1015), we investigate whether people display motivated reasoning when interpreting numerical information about the effects of refugee intake on crime rate. Our results show clear evidence of motivated reasoning along the lines of worldview ideology (i.e., whether people identify themselves primarily as nationally oriented or globally oriented). In scenarios where refugee intake was associated with higher crime rate, nationally oriented people were 18 percentage points more likely to make the correct assessment compared to globally oriented people. Likewise, in scenarios where refugee intake was associated with lower crime rate, nationally oriented people were 20 percentage points less likely to make the correct assessment compared to globally oriented people. Individuals with higher numeric ability were less likely to engage in motivated reasoning, suggesting that motivated reasoning more commonly is driven by feelings and emotional cues rather than deliberate analytical processes.

This paper evaluates the state of contact hypothesis research from a policy perspective. Building on Pettigrew and Tropp's (2006) influential meta-analysis, we assemble all intergroup contact studies that feature random assignment and delayed outcome measures, of which there are 27 in total, nearly two-thirds of which were published following the original review. We find the evidence from this updated dataset to be consistent with Pettigrew and Tropp's (2006) conclusion that contact “typically reduces prejudice.” At the same time, our meta-analysis suggests that contact's effects vary, with interventions directed at ethnic or racial prejudice generating substantially weaker effects. Moreover, our inventory of relevant studies reveals important gaps, most notably the absence of studies addressing adults' racial or ethnic prejudices, an important limitation for both theory and policy. We also call attention to the lack of research that systematically investigates the scope conditions suggested by Allport (1954) under which contact is most influential. We conclude that these gaps in contact research must be addressed empirically before this hypothesis can reliably guide policy.

There are inherent differences in the priorities of academics and policy-makers. These pose unique challenges for teams such as the Behavioural Insights Team (BIT), which has positioned itself as an organisation conducting academically rigorous behavioural science research in policy settings. Here we outline the threats to research transparency and reproducibility that stem from working with policy-makers and other non-academic stakeholders. These threats affect how we perform, communicate, verify and evaluate research. Solutions that increase research transparency include pre-registering study protocols, making data open and publishing summaries of results. We suggest an incentive structure (a simple ‘nudge’) that rewards BIT's non-academic partners for engaging in these practices.