Abstract Do people around us influence our personality? We investigate this question through a field experiment where we randomly assign university students to study groups. We find personality spillovers along three dimensions: students become more conscientious when assigned to conscientious peers, more open-minded when assigned to open-minded peers, and more competitive when assigned to competitive peers. We find no effects for peers' extraversion, agreeableness, or neuroticism. Our findings are consistent with students' adopting peer traits that are predictive of academic achievement. Our paper provides novel evidence on spillovers in noncognitive skills and establishes that socialization with peers affects personality development.

We study the long-term effects of a randomized intervention targeting children's socio-emotional skills. The classroom-based intervention for primary school children has positive impacts that persist for over a decade. Treated children become more likely to complete academic high school and enroll in university. Two mechanisms drive these results. Treated children show fewer ADHD symptoms: they are less impulsive and less disruptive. They also attain higher grades, but they do not score higher on standardized tests. The long-term effects on educational attainment thus appear to be driven by changes in socio-emotional skills rather than cognitive skills.

Life course epidemiology seeks to understand the intricate relationships between risk factors and health outcomes across different stages of life to inform prevention and intervention strategies to optimize health throughout the lifespan. However, extant evidence has predominantly been based on separate analyses of data from individual birth cohorts or panel studies, which may not be sufficient to unravel the complex interplay of risk and health across different contexts. We highlight the importance of a multi-study perspective that enables researchers to: (a) Compare and contrast findings from different contexts and populations, which can help identify generalizable patterns and context-specific factors; (b) Examine the robustness of associations and the potential for effect modification by factors such as age, sex, and socioeconomic status; and (c) Improve statistical power and precision by pooling data from multiple studies, thereby allowing for the investigation of rare exposures and outcomes. This integrative framework combines the advantages of multi-study data with a life course perspective to guide research in understanding life course risk and resilience on adult health outcomes by: (a) Encouraging the use of harmonized measures across studies to facilitate comparisons and synthesis of findings; (b) Promoting the adoption of advanced analytical techniques that can accommodate the complexities of multi-study, longitudinal data; and (c) Fostering collaboration between researchers, data repositories, and funding agencies to support the integration of longitudinal data from diverse sources. An integrative approach can help inform the development of individualized risk scores and personalized interventions to promote health and well-being at various life stages.

This paper investigates how exposure to higher-achieving male and female peers in university affects students’ major choices and labor market outcomes. For identification of causal effects, we exploit the random assignment of students to university sections in first-year compulsory courses. We present two main results. First, studying with higher-achieving peers has no statistically significant or economically meaningful effects on educational choices. Second, we find suggestive evidence that women who have been exposed to higher achieving male peers end up in jobs in which they are more satisfied.

Do the people around us influence our personality? To answer this question, we conduct an experiment with 543 university students who we randomly assign to study groups. Our results show that students become more similar to their peers along several dimensions. Students with more competitive peers become more competitive, students with more open-minded peers become more open-minded, and students with more conscientious peers become more conscientious. We see no significant effects of peers'extraversion, agreeableness, or neuroticism. To explain these results, we propose a simple model of personality development under the influence of peers. Consistent with the model's prediction, personality spillovers are concentrated in traits predictive of performance. Students adopt personality traits that are productive in the university context from their peers. Our findings highlight that socialization with peers can influence personality development.

Business degrees are popular and lead to high earnings. Female business graduates, however, earn less than their male counterparts. These gender differences can be traced back to university, where women shy away from majors like finance that lead to high earnings. In this paper, we investigate how the gender composition of peers in business school affects women’s and men’s major choices and labor market outcomes. We find that women who are randomly assigned to teaching sections with more female peers become less likely to choose male-dominated majors like finance and more likely to choose female-dominated majors like marketing. After graduation, these women end up in jobs where their earnings grow more slowly. Men, on the other hand, become more likely to choose male-dominated majors and less likely to choose female-dominated majors when they had more female peers in business school. However, men’s labor market outcomes are not significantly affected. Taken together, our results show that studying with more female peers in business school increases gender segregation in educational choice and affects labor market outcomes. This paper was accepted by Axel Ockenfels, decision analysis.

We study the effect of classroom rank on high school students' Big Five personality traits. We exploit idiosyncratic differences in the class distribution of earlier academic achievement. Such differences generate quasi-random variation in class rank for students with the same initial achievement. We find a positive and sizeable effect of rank on conscientiousness, but we find no effects on the other four personality traits. A thorough analysis of the mechanism suggests that the primary channels through which class rank improves conscientiousness are perceived ability and academic motivation.

This paper provides evidence of a novel facet of peer effects by showing that peer personality influences academic achievement. We exploit random assignment of students to university sections and find that students perform better in the presence of persistent peers. The impact of peer persistence is enduring, as students exposed to persistent peers at the beginning of their studies continue to achieve higher grades in subsequent periods. The personality peer effects that we document are distinct from other observable peer characteristics and suggest that peer personality traits affect human capital accumulation.

We investigate how high school gender composition affects students’ participation in STEM at college. Using Danish administrative data, we exploit idiosyncratic within-school variation in gender composition. We find that having a larger proportion of female peers reduces women’s probability of enrolling in and graduating from STEM programs. Men’s STEM participation increases with more female peers present. In the long run, women exposed to more female peers are less likely to work in STEM occupations, earn less, and have more children. Our findings show that the school peer environment has lasting effects on occupational sorting, the gender wage gap, and fertility.

This paper introduces peer value-added, a new approach to quantify the total contribution of an individual peer to student performance. Peer value-added captures social spillovers irrespective of whether they are generated by observable or unobservable peer characteristics. Using data with repeated random assignment to university sections, we find that students significantly differ in their peer value-added. Peer value-added is a good out-of-sample predictor of performance spillovers in newly assigned student-peer pairs. Yet, students’ own past performance and other observable characteristics are poor predictors of peer value-added. Peer value-added increases after exposure to better peers, and valuable peers are substitutes for low-quality teachers.

A substantial share of university instruction happens in tutorial sessions—small group instruction given parallel to lectures. In this paper, we study whether instructors with a higher academic rank teach tutorials more effectively in a setting where students are randomly assigned to tutorial groups. We find this to be largely not the case. Academic rank is unrelated to students' current and future performance and only weakly positively related to students' course evaluations. Building on these results, we discuss different staffing scenarios that show that universities can substantially reduce costs by increasingly relying on lower-ranked instructors for tutorial teaching.

This study exploits a large-scale natural experiment in Finnish conscription to study how exposure to peers from different family backgrounds affects education, earnings, employment, and hourly wage. Our research design is based on the alphabetic rule in assigning conscripts to dorms, which induces credible exogenous variation in peer family backgrounds. Being exposed to a dormmate from a highincome family has a positive long-term effect on earnings. The effects are the largest for individuals who come from high-income families. Exposure to peers with one standard deviation higher average parent income raises their earnings at age 28-42 by 2.6%. The results suggest beneficial labor market networks as a key mechanism. Exposure to peers from high-income families has little impact on earnings and hourly wages of individuals who come from low-income families, but it increases their educational attainment in the long run. The findings imply that social stratification reinforces economic and educational inequality between rich and poor families.

In a previous paper, we have shown that academic rank is largely unrelated to tutorial teaching effectiveness. In this paper, we further explore the effectiveness of the lowest-ranked instructors: students. We confirm that students are almost as effective as senior instructors, and we produce results informative on the effects of expanding the use of student instructors. We conclude that hiring moderately more student instructors would not harm students, but exclusively using them will likely negatively affect student outcomes. Given how inexpensive student instructors are, however, such a policy might still be worth it.

This paper investigates how achievement of university peers affects men’s and women’s course choices, major choices, and labor market outcomes. Exploiting random assignment of students to sections, we find that higher-achieving male peers cause men to take more mathematical courses. This effect persists in the labor market where men end up in higher-paying jobs. Women with higher- achieving male peers choose fewer mathematical courses and majors. These women end up in jobs where they earn less but are more satisfied. Thus, it is not obvious whether women’s exposure to high-achieving male peers benefits or harms them.

This paper investigates how the peer gender composition in university affects students’ major choices and labor market outcomes. Women who are randomly assigned to more female peers become less likely to choose male-dominated majors, and they end up in jobs in which they work fewer hours and earn less. Men become more likely to choose male-dominated majors after having had more female peers, although their labor market outcomes are not affected. Our results suggest that the increasing female university enrollment over recent decades has paradoxically contributed to the occupational segregation among university graduates that persists in today’s labor market.

In this paper we study how a student's ordinal rank in a peer group affects performance and specialisation choices in university. By exploiting data with repeated random assignment of students to teaching sections, we find that a higher rank increases performance and the probability of choosing related follow-up courses and majors. We document two types of dynamic effect. First, earlier ranks are less important than later ranks. Second, responses to rank changes are asymmetric: improvements in rank raise performance, while decreases in rank have no effect. Rank effects partially operate through students’ expectations about future grades.