Megastudy shows that reminders boost vaccination but adding free rides does not.

Encouraging routine COVID-19 vaccinations is likely to be a crucial policy challenge for decades to come. To avert hundreds of thousands of unnecessary hospitalizations and deaths, adoption will need to be higher than it was in the autumn of 2022 or 2023, when less than one-fifth of Americans received booster vaccines1,2. One approach to encouraging vaccination is to eliminate the friction of transportation hurdles. Previous research has shown that friction can hinder follow-through3 and that individuals who live farther from COVID-19 vaccination sites are less likely to get vaccinated4. However, the value of providing free round-trip transportation to vaccination sites is unknown. Here we show that offering people free round-trip Lyft rides to pharmacies has no benefit over and above sending them behaviourally informed text messages reminding them to get vaccinated. We determined this by running a megastudy with millions of CVS Pharmacy patients in the United States testing the effects of (1) free round-trip Lyft rides to CVS Pharmacies for vaccination appointments and (2) seven different sets of behaviourally informed vaccine reminder messages. Our results suggest that offering previously vaccinated individuals free rides to vaccination sites is not a good investment in the United States, contrary to the high expectations of both expert and lay forecasters. Instead, people in the United States should be sent behaviourally informed COVID-19 vaccination reminders, which increased the 30-day COVID-19 booster uptake by 21% (1.05 percentage points) and spilled over to increase 30-day influenza vaccinations by 8% (0.34 percentage points) in our megastudy. More rigorous testing of interventions to promote vaccination is needed to ensure that evidence-based solutions are deployed widely and that ineffective but intuitively appealing tools are discontinued.

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.

What can machine learning teach us about habit formation? Evidence from exercise and hygiene.

We apply a machine learning technique to characterize habit formation in two large panel data sets with objective measures of 1) gym attendance (over 12 million observations) and 2) hospital handwashing (over 40 million observations). Our Predicting Context Sensitivity (PCS) approach identifies context variables that best predict behavior for each individual. This approach also creates a time series of overall predictability for each individual. These time series predictability values are used to trace a habit formation curve for each individual, operationalizing the time of habit formation as the asymptotic limit of when behavior becomes highly predictable. Contrary to the popular belief in a "magic number" of days to develop a habit, we find that it typically takes months to form the habit of going to the gym but weeks to develop the habit of handwashing in the hospital. Furthermore, we find that gymgoers who are more predictable are less responsive to an intervention designed to promote more gym attendance, consistent with past experiments showing that habit formation generates insensitivity to reward devaluation.

A national experiment reveals where a growth mindset improves achievement.

A global priority for the behavioural sciences is to develop cost-effective, scalable interventions that could improve the academic outcomes of adolescents at a population level, but no such interventions have so far been evaluated in a population-generalizable sample. Here we show that a short (less than one hour), online growth mindset intervention-which teaches that intellectual abilities can be developed-improved grades among lower-achieving students and increased overall enrolment to advanced mathematics courses in a nationally representative sample of students in secondary education in the United States. Notably, the study identified school contexts that sustained the effects of the growth mindset intervention: the intervention changed grades when peer norms aligned with the messages of the intervention. Confidence in the conclusions of this study comes from independent data collection and processing, pre-registration of analyses, and corroboration of results by a blinded Bayesian analysis.

A 680,000-person megastudy of nudges to encourage vaccination in pharmacies.

Encouraging vaccination is a pressing policy problem. To assess whether text-based reminders can encourage pharmacy vaccination and what kinds of messages work best, we conducted a megastudy. We randomly assigned 689,693 Walmart pharmacy patients to receive one of 22 different text reminders using a variety of different behavioral science principles to nudge flu vaccination or to a business-as-usual control condition that received no messages. We found that the reminder texts that we tested increased pharmacy vaccination rates by an average of 2.0 percentage points, or 6.8%, over a 3-mo follow-up period. The most-effective messages reminded patients that a flu shot was waiting for them and delivered reminders on multiple days. The top-performing intervention included two texts delivered 3 d apart and communicated to patients that a vaccine was "waiting for you." Neither experts nor lay people anticipated that this would be the best-performing treatment, underscoring the value of simultaneously testing many different nudges in a highly powered megastudy.

A megastudy of text-based nudges encouraging patients to get vaccinated at an upcoming doctor's appointment.

Many Americans fail to get life-saving vaccines each year, and the availability of a vaccine for COVID-19 makes the challenge of encouraging vaccination more urgent than ever. We present a large field experiment (N = 47,306) testing 19 nudges delivered to patients via text message and designed to boost adoption of the influenza vaccine. Our findings suggest that text messages sent prior to a primary care visit can boost vaccination rates by an average of 5%. Overall, interventions performed better when they were 1) framed as reminders to get flu shots that were already reserved for the patient and 2) congruent with the sort of communications patients expected to receive from their healthcare provider (i.e., not surprising, casual, or interactive). The best-performing intervention in our study reminded patients twice to get their flu shot at their upcoming doctor's appointment and indicated it was reserved for them. This successful script could be used as a template for campaigns to encourage the adoption of life-saving vaccines, including against COVID-19.

Sparking Virtuous Cycles: A Longitudinal Study of Subjective Well-Being and Grit During Early Adolescence.

In cross-sectional research, subjective well-being and grit are found to be positively correlated. Their mutually reinforcing effects are particularly relevant for youth entering early adolescence because, during this developmental period, both well-being and grit have been shown to predict consequential outcomes later in life. However, their mutual relation has not yet been investigated in early adolescence. This study, therefore, examined the possibility of a virtuous cycle linking subjective well-being and grit during early adolescence. Self-report questionnaires of grit and subjective well-being were completed by N = 5291 children in China (47.6% girls; initial Mage = 9.69, SDage = 0.59) on six occasions over 3 academic years. In random-intercept cross-lagged panel models (RI-CLPMs), within-person changes in grit predicted within-person changes in subjective well-being 6 months later, and vice versa. Notably, analyses revealed an asymmetry in this cycle: paths from subjective well-being to grit were stronger and more reliable than the converse. Likewise, facet-level analyses showed that the predictive power of the perseverance component (of grit) and the affective component (of subjective well-being), respectively, was greater than the passion and cognitive components, respectively. These findings highlight the potential of boosting happiness for catalyzing positive youth development and, in addition, foreground the utility of studying these composite constructs at the facet level.

Daily fluctuations in young children's persistence.

Children's behavior changes from day to day, but the factors that contribute to its variability are understudied. We developed a novel repeated measures paradigm to study children's persistence by capitalizing on a task that children complete every day: toothbrushing (N = 81; 48% female; 36-47 months; 80% white, 14% Multiracial, 10% Hispanic, 2% Asian, 1% Black; 1195 observations collected between January 2019 and March 2020). Children brushed longer on days when their parents used more praise (d = .23) and less instruction (d = -.22). Sensitivity to mood, sleep, and parent stress varied across children, suggesting that identifying the factors that shape an individual child's persistence could lead to personalized interventions.

The development of grit and growth mindset in Chinese children.

In a recent longitudinal study of U.S. adolescents, grit predicted rank-order increases in growth mindset and, to a lesser degree, growth mindset predicted rank-order increases in grit. The current investigation replicated and extended these findings in a younger non-Western, educated, industrialized, rich, and democratic (non-WEIRD) population. Two large samples totaling more than 5000 elementary school children in China completed self-report questionnaires assessing grit and growth mindset five times over 2 years. As in Park et al. (2020, Journal of Experimental Child Psychology, 198, 1048892020), we found reciprocal relations between grit and growth mindset. Grit systematically predicted rank-order increases in growth mindset at each subsequent 6-month interval. Growth mindset also predicted small rank-order increases in grit over the same period. These findings suggest that, over time, behavior may exert as much an influence on beliefs as the reverse-a dynamic possibly observable as early as in elementary school and not just in WEIRD cultures.

A large-scale field experiment shows giving advice improves academic outcomes for the advisor.

Common sense suggests that people struggling to achieve their goals benefit from receiving motivational advice. What if the reverse is true? In a preregistered field experiment, we tested whether giving motivational advice raises academic achievement for the advisor. We randomly assigned n = 1,982 high school students to a treatment condition, in which they gave motivational advice (e.g., how to stop procrastinating) to younger students, or to a control condition. Advice givers earned higher report card grades in both math and a self-selected target class over an academic quarter. This psychologically wise advice-giving nudge, which has relevance for policy and practice, suggests a valuable approach to improving achievement: one that puts people in a position to give.

Cognitive and noncognitive predictors of success.

When predicting success, how important are personal attributes other than cognitive ability? To address this question, we capitalized on a full decade of prospective, longitudinal data from n = 11,258 cadets entering training at the US Military Academy at West Point. Prior to training, cognitive ability was negatively correlated with both physical ability and grit. Cognitive ability emerged as the strongest predictor of academic and military grades, but noncognitive attributes were more prognostic of other achievement outcomes, including successful completion of initiation training and 4-y graduation. We conclude that noncognitive aspects of human capital deserve greater attention from both scientists and practitioners interested in predicting real-world success.

The mixed effects of online diversity training.

We present results from a large (n = 3,016) field experiment at a global organization testing whether a brief science-based online diversity training can change attitudes and behaviors toward women in the workplace. Our preregistered field experiment included an active placebo control and measured participants' attitudes and real workplace decisions up to 20 weeks postintervention. Among groups whose average untreated attitudes-whereas still supportive of women-were relatively less supportive of women than other groups, our diversity training successfully produced attitude change but not behavior change. On the other hand, our diversity training successfully generated some behavior change among groups whose average untreated attitudes were already strongly supportive of women before training. This paper extends our knowledge about the pathways to attitude and behavior change in the context of bias reduction. However, the results suggest that the one-off diversity trainings that are commonplace in organizations are unlikely to be stand-alone solutions for promoting equality in the workplace, particularly given their limited efficacy among those groups whose behaviors policymakers are most eager to influence.

Revisiting the Factor Structure of Grit: A Commentary on Duckworth and Quinn (2009).

This commentary addresses debate over the factor structure of the Grit Scale in both its original and short forms. Commonly (and in our own work), factor solutions are used to establish dimensionality of the construct being measured. For example, a two-factor hierarchical model was proposed for the Short Grit Scale. It has since been pointed out, correctly, that the specified model cannot be distinguished from a model with two correlated subfactors and no higher-order factor. In this commentary, we acknowledge the mathematical equivalence of these specifications and our error in interpretation. However, we also take the opportunity to admit a more profound correction. It is now clear to us that statistical answers cannot definitively settle certain theoretical riddles, and our argument for grit as a compound of related but distinct dispositions should not have relied so heavily on the optimal factor solution for a questionnaire devised to assess it. Rather, a conceptual question demands a conceptual answer, which we briefly attempt here. We conclude by noting the need for improved operationalizations of the tendency to stay committed to goals for years (passion) while working assiduously toward their achievement (perseverance).

Beyond willpower.

For all its popularity as a psychological construct, willpower is irremediably polysemous. A more helpful construct is self-control, defined as the self-regulation of conflicting impulses. We show how the process model of self-control provides a principled framework for examining how undesirable impulses may be weakened and desirable impulses may be strengthened.

Self-Control and Academic Achievement.

Self-control refers to the alignment of thoughts, feelings, and actions with enduringly valued goals in the face of momentarily more alluring alternatives. In this review, we examine the role of self-control in academic achievement. We begin by defining self-control and distinguishing it from related constructs. Next, we summarize evidence that nearly all students experience conflict between academic goals that they value in the long run and nonacademic goals that they find more gratifying in the moment. We then turn to longitudinal evidence relating self-control to academic attainment, course grades, and performance on standardized achievement tests. We use the process model of self-control to illustrate how impulses are generated and regulated, emphasizing opportunities for students to deliberately strengthen impulses that are congruent with, and dampen impulses that are incongruent with, academic goals. Finally, we conclude with future directions for both science and practice.

The development of grit and growth mindset during adolescence.

Individual differences in grit and growth mindset predict effort and achievement in the face of challenges, but little is known about how the two traits influence each other during adolescence. In the current investigation, we analyzed data on grit and growth mindset collected from 1667 adolescents and their teachers on four occasions over 2 academic years. In autoregressive cross-lagged models, grit predicted rank-order increases in growth mindset and growth mindset predicted rank-order increases in grit. These findings suggest that during adolescence, grit and growth mindset are distinct but mutually reinforcing.

How Does High School Extracurricular Participation Predict Bachelor's Degree Attainment? It is Complicated.

This study answered novel questions about the connection between high school extracurricular dosage (number of activities and participation duration) and the attainment of a bachelor's degree. Using data from the Common Application and the National Student Clearinghouse (N = 311,308), we found that greater extracurricular participation positively predicted bachelor's degree attainment. However, among students who ultimately earned a bachelor's degree, participating in more than a moderate number of high school activities (3 or 4) predicted decreasing odds of earning a bachelor's degree on time (within 4 years). This effect intensified as participation duration increased, such that students who participated in the greatest number of high school activities for the most years were the most likely to delay college graduation.

Dear Abby: Should I Give Advice or Receive It?

Typically, individuals struggling with goal achievement seek advice. However, in the present investigation ( N = 2,274), struggling individuals were more motivated by giving advice than receiving it. In a randomized, controlled, double-blind field experiment, middle-school students who gave motivational advice to younger students spent more time on homework over the following month than students who received motivational advice from expert teachers (Experiment 1). This phenomenon was replicated across self-regulatory domains: Strugglers who gave advice, compared with those who received expert advice, were more motivated to save money, control their tempers, lose weight, and seek employment (Experiments 2 and 3). Nevertheless, across domains, people erroneously predicted the opposite, expecting themselves and others to be less motivated by giving advice than receiving it (Experiments 2 and 3). Why are people blind to the motivational power of giving? Giving advice motivated givers by raising their confidence-a reality that predictors fail to anticipate (Experiment 4).

Beliefs About Stress Attenuate the Relation Among Adverse Life Events, Perceived Distress, and Self-Control.

Prior research has shown that adverse events in the lives of adolescents precipitate psychological distress, which in turn impairs self-control. This study (N = 1,343) examined the protective effects of stress mindsets-beliefs about the extent to which stress might be beneficial or strictly detrimental. The results confirmed that increasing the number of adverse life events across the school year predicted rank order increases in perceived distress, which in turn predicted rank order decreases in self-control. Adolescents who believed in the potential benefits of stress were less prone to feeling stressed in the wake of adverse life events. These findings suggest that changing the way adolescents think about stress may help protect them from acting impulsively when confronted with adversity.

Too much of a good thing? Exploring the inverted-U relationship between self-control and happiness.

OBJECTIVE: Can having too much self-control make people unhappy? Researchers have increasingly questioned the unilateral goodness of self-control and proposed that it is beneficial only up to a certain point, after which it becomes detrimental. The little empirical research on the issue shows mixed results. Hence, we tested whether a curvilinear relationship between self-control and subjective well-being exists. METHOD: We used multiple metrics (questionnaires, behavioral ratings), sources (self-report, other-report), and methods (cross-sectional measurement, dayreconstruction method, experience sampling method) across six studies (Ntotal = 5,318). RESULTS: We found that self-control positively predicted subjective well-being (cognitive and affective), but there was little evidence for an inverted U-shaped curve. The results held after statistically controlling for demographics and other psychological confounds. CONCLUSION: Our main finding is that self-control enhances subjective well-being with little to no apparent downside of too much self-control.