Peer effects and health impacts of different body cognitive biases in children: micro evidence from China

Background

In China, children commonly display body cognitive biases, which constitute a significant yet hidden public health issue. These biases potentially jeopardize children's well-being, hinder the cultivation of human capital, and impede societal progress. However, limited research employs theoretical analysis and econometric testing to investigate the formation of different body cognitive biases among Chinese children and their health impacts.

Methods

Based on a local average network model for theoretical analysis, this study utilizes a sample of 4,289 children from four phases of the China Health and Nutrition Survey (CHNS) conducted from 2004 to 2011. Utilizing Logit and IV Probit models, systematically evaluate the peer effect, heterogeneity of effects, and health impacts of children's different body cognitive biases.

Results

(1) The peer effect contributes to the development of light- and heavy-body cognitive biases in Chinese children. (2) The heterogeneity analysis shows that the peer effect of body cognitive biases is more significant in rural and female children. (3) The influence of heavy-body cognitive bias is more pronounced in adolescent children. (4) The "eating-activity balance" is disrupted by the two body cognitive biases in children, leading to deviations from normal body type. (5) Specifically, the light-body cognitive bias leads children to intake more and burn fewer calories, increasing their risk of obesity. (6) Conversely, the heavy-body cognitive bias prompts children to intake less and expend more calories, resulting in a higher prevalence of thinness.

Discussion

This study innovates by exploring peer effects on body cognitive biases in Chinese children, elucidating their direction and health implications. While overweight and obesity are recognized as overt health issues, the spread and impact of implicit issues like body cognitive biases should not be overlooked. Nevertheless, the issue is largely neglected in developing countries, such as China, where existing children's health policies are inadequate in addressing it. Promoting accurate body image perception and understanding of health prevention strategies among children requires adequate attention to peer effects.

Effects of Online Friendships on Safer Sex Communication and Behavior among Black Sexual Minority Men: A Study of Network Exposure

This study draws on social normative and social learning theories to examine the masspersonal safer sex communication (i.e., Facebook posts about safer sex) and safer sex behavior (i.e., condom use) in a cohort of Black sexual minority men (BSMM) (N = 340), with an eye toward understanding their relationship with the safer sex communication and behaviors of their BSMM Facebook friends. Using linear network autocorrelation regression models, results showed that BSMM's safer sex communication and condom use behavior were each associated with the communication and behavior of their online peers. Specifically, BSMM's condom use was positively associated with their friends' condom use and friends' safer sex communication, and BSMMs' safer sex communication was positively associated with friends' safer sex communication. Moreover, contrary to prior research, BSSM's safer sex communication and condom use were not related to one another, suggesting that talking about safer sex on social media should not be interpreted to be an indication of engageDment in safer sex behavior. These findings underscore an opportunity to leverage peer influence in social media networks, particularly in the form of masspersonal communication, to encourage cascades of safer sex messaging among peers and adoption of safer sex behavior.

Influence of caregiver input and language experience on the production of coda laterals by English-Malay bilingual preschoolers in multi-accent Singapore

Linguistic input in multi-lingual/-cultural contexts is highly variable. We examined the production of English and Malay laterals by fourteen early bilingual preschoolers in Singapore who were exposed to several allophones of coda laterals: Malay caregivers use predominantly clear-l in English and Malay, but their English coda laterals can also be l-less (vocalised/deleted) and in formal contexts, velarised. Contrastingly, the English coda laterals of the Chinese majority are typically l-less. Findings show that English coda laterals were overall more likely to be l-less than Malay laterals like their caregivers', but English coda laterals produced by children with close Chinese peer(s) were more likely to be l-less than those without. All children produced English coda clear-l, demonstrating the transmission of an ethnic marker that had emerged from long-term contact. In diverse settings, variation is intrinsic to the acquisition process, and input properties and language experience are important considerations in predicting language outcomes.

Role of Peer Effects in China's Energy Transition: Evidence from Rural Beijing

China's efforts to encourage energy transition from coal to cleaner methods of space heating have gained great achievement. However, not all progress met expectations; that is, some households still rely on solid fuel. Sociocultural factors provide one plausible explanation. While existing studies have examined and quantified the socioeconomic factors, little attention has been paid to the peer effects that are often critical in the Chinese cultural context. This study first presents household energy consumption patterns using household-level data on the coal-switching program in rural Beijing. It shows that the coal-switching program did not completely eliminate the use of solid fuel for space heating as expected. To explore the underlying determinants, we apply an econometric model of the forces driving energy transition, focusing on peer effects. The results confirm that the coal-switching program significantly reduces the use of solid fuel. Moreover, it reveals that the peer effect, measured by the average village-level solid fuel use rate, matters for households' fuel choices. We also find that the peer effect varies with different income levels and policies. These findings provide new evidence and insights for future policy design.

Targeted maximum likelihood estimation of causal effects with interference: A simulation study

Interference, the dependency of an individual's potential outcome on the exposure of other individuals, is a common occurrence in medicine and public health. Recently, targeted maximum likelihood estimation (TMLE) has been extended to settings of interference, including in the context of estimation of the mean of an outcome under a specified distribution of exposure, referred to as a policy. This paper summarizes how TMLE for independent data is extended to general interference (network-TMLE). An extensive simulation study is presented of network-TMLE, consisting of four data generating mechanisms (unit-treatment effect only, spillover effects only, unit-treatment and spillover effects, infection transmission) in networks of varying structures. Simulations show that network-TMLE performs well across scenarios with interference, but issues manifest when policies are not well-supported by the observed data, potentially leading to poor confidence interval coverage. Guidance for practical application, freely available software, and areas of future work are provided.

Effects of Conformity Tendencies on Farmers' Willingness to Take Measures to Respond to Climate Change: Evidence from Sichuan Province, China

Encouraging farmers to respond to climate change is very important for agricultural production and environmental governance. Based on the data of 540 farmers in Sichuan Province, China, the effects of conformity tendencies on farmers' adaptive behavior decisions to climate change were analyzed using the binary logistic model and propensity score matching method (PSM). The results show that (1) relatives' and friends' adaptive behaviors to climate change positively affect farmers' adaptive behaviors to climate change. (2) Compared with relatives and friends who do not visit each other during the New Year (weak ties), the climate change adaptation behavior of relatives and friends who visit each other during the New Year (strong ties) has a more significant impact on the climate change adaptation behavior of farmers. (3) Farmers with higher education levels and agricultural products without disaster experience are more significantly affected by peer effects and more inclined to take measures to respond to climate change. (4) Social networks and social trust play a partially mediating role in the peer effects of farmers' adaptation to climate change, but there are differences between relatives and friends with different strong and weak ties.

Short-run and Long-run Effects of Peers from Disrupted Families

I study the short-run and long-run effects of exposure to peers from disrupted families in adolescence. Using the National Longitudinal Study of Adolescent to Adult Health (Add Health) data, I find that girls are mostly unaffected by peers from disrupted families, while boys exposed to more peers from disrupted families exhibit more school problems in adolescence and higher arrest probabilities, less stable jobs and higher probabilities of suffering from financial stress as young adults. These results suggest negative effects on non-cognitive skills but no effect on cognitive skills, as measured by academic performance. The dramatic increase in family disruption in the United States should thus receive more attention, as the intergenerational mobility and inequality consequences could be larger than anticipated as a result of classroom spillovers.

Contagious COVID-19 policies: Policy diffusion during times of crisis

The COVID-19 crisis demanded rapid, widespread policy action. In response, nations turned to different forms of social distancing policies to reduce the spread of the virus. These policies were implemented globally, proving as contagious as the virus they are meant to prevent. Yet, variation in their implementation invites questions as to how and why countries adopt social distancing policies, and whether the causal mechanisms driving these policy adoptions are based on internal resources and problem conditions or other external factors such as conditions in other countries. We leverage daily changes in international social distancing policies to understand the impacts of problem characteristics, institutional and economic context, and peer effects on social distancing policy adoption. Using fixed-effects models on an international panel of daily data from 2020, we find that peer effects, particularly mimicry of geographic neighbors, political peers, and language agnates drive policy diffusion and shape countries' policy choices.

Health Shocks and Household Education Burden-A Study From the Perspective of Relative Poverty Alleviation in China

Health shocks and household education burden influence levels of expenditure on healthcare and education, which are two major non-discretionary expenditures for households. From the perspective of relative poverty alleviation in China and based on the peer effects theory, this study uses the dataset from the rural areas in CFPS database and employs the spatial Durbin model and spatial DID model to investigate-when a household suffers health shocks-the influence of such impact on the education burden of closely related households and to test the effect of single rescue policy in this circumstance. Further, this study employs a spatial mediating effect model to analyze the spatial transmission mechanism. The results indicate that when a household has health shocks, it can aggravate the education burden of closely related households through inter-household social networks. The findings substantiate that the targets of different rescue policies have cross effects and that single rescue policy does not have significant effect on the targets of other policies. To avoid the situation where rescue policies operate in silos and to reduce the internal coordination cost between different policies within a system, a coordinating mechanism should be established between different rescue policies to better alleviate relative poverty.

Drug Diffusion Through Peer Networks: The Influence of Industry Payments

Pharmaceutical companies market to physicians through individual detailing accompanied by monetary or in-kind transfers. Large compensation payments to a small number of physicians account for most of this promotional spending. Studying US promotional payments and prescriptions for anticoagulant drugs, we investigate how peer influence broadens the payments' reach. Following a compensation payment, prescriptions for the marketed drug increase by both the paid physician and the paid physician's peers. Payments increase prescriptions to both recommended and contraindicated patients. Over three years, marketed anticoagulant prescriptions rose 23 percent due to payments, with peer spillovers contributing a quarter of the increase.

Preferences for a mixed-sex composition of offspring: A multigenerational approach

Parents with two boys or two girls are more likely to have a third child than those with a 'sex mix'. However, little is known on whether these 'mixed-sex preferences' extend beyond the nuclear family. This study leverages the random variation in sex at birth to assess whether the sex of nieces and nephews, in combination with own children, matters for fertility choices. Using three-generational data from the US Panel Study of Income Dynamics (PSID), I show that extended families (including grandparents, their children, and their grandchildren) are collectively more likely to have three or more grandchildren when lacking sex mix, whether the first two grandchildren are siblings or cousins. I explore the pathways for these offspring sex preferences, finding support for a preference for an uninterrupted line of male descendants. This multigenerational approach also contributes a new estimation strategy that causally estimates the effects of family sizes on outcomes beyond fertility.

Adolescent school injuries and classroom sex compositions in German secondary schools

BACKGROUND

School injuries are an important adolescent health problem. Previous research suggests that relevant risk behaviors for school injuries, risk-taking and aggression, are highly susceptible to peer effects. Specifically, evidence suggests that the ratio of men and women in peer groups (sex ratio) affects individuals' propensity for aggression and risk-taking. However, potential associations of classroom sex ratios with adolescent school injury risks have not been studied so far. The purpose of this paper is to investigate the association of classroom sex compositions with adolescent school injuries.

METHODS

We investigate the association of classroom sex ratios with school injuries in a longitudinal survey dataset containing 13,131 observations from 9,204 adolescent students (ages 13-16) from secondary schools in Germany. The data also allow us to identify injuries due to aggressive behavior and analyze these injuries in detail. We use multilevel logistic regression models to analyze risks of both overall and aggression-related school injuries.

RESULTS

Adolescent students' risk for school injuries is significantly and positively associated with male-skewed classroom sex ratios (OR = 1.012, p=0.012). Specifically, the risk of sustaining a school injury increases by 33.5 percent when moving from the 10th to the 90th classroom sex ratio percentile. Moreover, we find an even stronger positive association between male-dominated classrooms and aggression-related injury risks (OR = 1.022, p=0.010). Compared to classroom sex ratios at the 10th percentile, the risk of an aggression-related injury is 78 percent higher in classrooms with a sex ratio at the 90th percentile. Finally, we find that both boys' and girls' injury risks equally increase with a higher proportion of male students in their classroom.

CONCLUSIONS

Our findings indicate that sex composition of classrooms is an important contextual factor for adolescent school injuries, in particular school injuries resulting from aggression. These findings illustrate the need to integrate a contextual perspective on school injuries among adolescent students both into research and into intervention planning.

Peer Effects on Engagement and Disengagement: Differential Contributions From Friends, Popular Peers, and the Entire Class

School engagement and disengagement are important predictors of school success that are grounded in the social context of the classroom. This study used multilevel analysis to examine the contributions of the descriptive norms of friends, popular students and classmates regarding engagement and disengagement to the development of Students' own behavioral and emotional engagement and disengagement among Flemish 7th-graders (N = 3,409). Moderating effects of Students' self-esteem and cognitive ability were examined. The results showed effects from friends' and classmates' (dis)engagement on all dimensions of (dis)engagement. Popular Students' engagement only affected individual Student's behavioral disengagement and emotional engagement. Self-esteem and high cognitive ability did not make students more or less susceptible to peer effects.

General regression methods for respondent-driven sampling data

Respondent-driven sampling is a variant of link-tracing sampling techniques that aim to recruit hard-to-reach populations by leveraging individuals’ social relationships. As such, a respondent-driven sample has a graphical component which represents a partially observed network of unknown structure. Moreover, it is common to observe homophily, or the tendency to form connections with individuals who share similar traits. Currently, there is a lack of principled guidance on multivariate modelling strategies for respondent-driven sampling to address peer effects driven by homophily and the dependence between observations within the network. In this work, we propose a methodology for general regression techniques using respondent-driven sampling data. This is used to study the socio-demographic predictors of HIV treatment optimism (about the value of antiretroviral therapy) among gay, bisexual and other men who have sex with men, recruited into a respondent-driven sampling study in Montreal, Canada.

Peer Effects on Real-Time Search Behavior in Experimental Stock Markets

It is a well-documented phenomenon that individuals stop searching earlier than predicted by the optimal, risk-neutral stopping rule, leading to inefficient searches. Individuals' search behaviors during making investment decisions in financial markets can be easily affected by their peers. In this study, we designed a search game in a simplified experimental stock market in which subjects were required to search for the best sell prices for their stocks. By randomly assigning subjects into pairs and presenting them with real-time information on their peers' searches, we investigated the effects of peers' decisions on search behaviors. The results showed that two subjects in the same group with real-time peer information learned and engaged in similar search behaviors. However, this peer effect did not exist when subjects had access to feedback information on the ex-post best response. In addition, we found that the presence of information about peers' decisions alone had no significant impact on search efficiency, whereas access to both information on peers' decisions and feedback information significantly improved subjects' search efficiency.

Dying from envy: The role of inequality

We hypothesize that when interpersonal comparisons, often referred to as "keeping up with the Joneses", are operational, relative deprivation (income inequality) results in increased likelihood of morbidity among lower income households. Using a simple theoretical model, we show that the larger the income disparities between "the Joneses" and "the followers", the higher is the followers' expenditure on conspicuous consumption and the lower is their expenditure on health. We empirically test our hypotheses using Canadian data from the Canadian Community Health Survey and the Survey of Household Spending and US data from the National Health Interview Survey. We find that, in peer groups defined by geographic proximity of residence or similar socio-economic background, larger income disparities are associated with higher spending by the followers on conspicuous consumption, lower health expenditure, worse self-reported health and younger age at death.

Spatial Characteristics of the Diffusion of Residential Solar Photovoltaics in Urban Areas: A Case of Seoul, South Korea

Mini-solar photovoltaics, which are installed on apartment balconies, are rapidly spreading in Seoul, South Korea. Seoul has implemented a policy to diffuse mini-solar photovoltaics in apartments for energy transition since 2012. The policy considers compact land use and a large population of the city. This study examines a variety of variables in relation to the adoption of mini-solar photovoltaics. In particular, we focus on peer effects, namely, those of spatially adjacent, previously installed mini-solar photovoltaics. As apartment characteristics, four variables are selected to assess both within and between apartment complexes: one for the density of adopters as a within-complex variable and three for the number of adopters in the 500 m, 1 km, and 1.5 km radius of apartment complexes as between-complex variables. A major finding is that peer effects significantly contribute to the new adoption of mini-solar photovoltaics. Implications of this finding are discussed in an urban context.

Interdependence and the cost of uncoordinated responses to COVID-19

Social distancing is the core policy response to coronavirus disease 2019 (COVID-19). But, as federal, state and local governments begin opening businesses and relaxing shelter-in-place orders worldwide, we lack quantitative evidence on how policies in one region affect mobility and social distancing in other regions and the consequences of uncoordinated regional policies adopted in the presence of such spillovers. To investigate this concern, we combined daily, county-level data on shelter-in-place policies with movement data from over 27 million mobile devices, social network connections among over 220 million Facebook users, daily temperature and precipitation data from 62,000 weather stations, and county-level census data on population demographics to estimate the geographic and social network spillovers created by regional policies across the United States. Our analysis shows that the contact patterns of people in a given region are significantly influenced by the policies and behaviors of people in other, sometimes distant, regions. When just one-third of a state's social and geographic peer states adopt shelter-in-place policies, it creates a reduction in mobility equal to the state's own policy decisions. These spillovers are mediated by peer travel and distancing behaviors in those states. A simple analytical model calibrated with our empirical estimates demonstrated that the "loss from anarchy" in uncoordinated state policies is increasing in the number of noncooperating states and the size of social and geographic spillovers. These results suggest a substantial cost of uncoordinated government responses to COVID-19 when people, ideas, and media move across borders.

Self-selecting peer groups formed within the laboratory environment have a lasting effect on individual student attainment and working practices

Within the present study, we investigate the lasting effect of laboratory peer group interactions on the end of year attainment of Biosciences and Chemistry students. By asking students to identify who they primarily work with within the laboratory environment and evaluating the interactions through cluster analysis, we identified two main categories of laboratory peer groups: the first long-lived well-established pairings of two students, 'swans', who work together for all or the majority of the laboratory sessions; and the second dynamic fluid groups, 'dolphins', of between three and nine students who work with each other interchangeably. Statistical analysis is presented, which demonstrates that individuals within each laboratory peer group were likely to achieve a similar average mark at the end of the first year of study on the course. We identified the driving factors for the formation of these groups as friendship and perceived work ethic. There is a preference for high-achieving students to work with other high-achieving students and lower-achieving to group around a shared social background. Targeted interventions, in which pairings were selected by the tutor at the onset of the study, altered the ratio from long-lived pairs to more dynamic groups and increased students' willingness to work with others outside of their group but did not change the drivers of group formation or resulting pattern of achievement. We conclude with recommendations around group working within the laboratory environment.

Perpetration of Adolescent Dating Relationship Abuse: The Role of Conditional Tolerance for Violence and Friendship Factors

Research has pointed to the salience of friendships in predicting abuse in adolescent dating relationships. The current study investigates the perpetration of physical and sexual dating abuse as predicted by individual conditional tolerance for dating abuse within the context of friendship behaviors and group characteristics. Using two waves of the National Survey of Teen Relationships and Intimate Violence (STRiV; N = 511 daters aged 12-18 years), we investigated the effects of baseline individual tolerance for hitting dating partners and friendship factors on perpetration of physical and sexual adolescent dating abuse (ADA) approximately 1 year later. Conditional tolerance for hitting boyfriends was associated with ADA perpetration in the absence of friendship characteristics. Daters who reported recent discussion of a problem with friends and female daters who named all-girl friendship groups were more likely to report ADA perpetration. Close friendships are an avenue for preventing ADA perpetration. Furthermore, ADA perpetration may be reduced by targeting conditional tolerance for violence particularly against male partners within female friendship groups.

Roommate effects in health outcomes

We use randomized roommate assignment in dormitories in a college in Kolkata in India to examine peer effects in weight gains among roommates. We use administrative data on weight, height, and test scores of students at the time of college admission and then survey these students at the end of their first and second years in college. We do not find any significant roommate specific peer effect in weight gain. Our results rather suggest that an obese roommate reduces the probability that the other roommates become obese in subsequent years. We examine potential mechanism using survey data on students' eating habits, smoking, exercise, and sleeping patterns. We find that obese roommates sleep longer, which in turn improves the sleep pattern of others, which might explain the weak negative effect of obese roommates on the weight of others in the same room.

Testing for family influences on obesity: The role of genetic nurture

A large literature has documented strong positive correlations among siblings in health, including body mass index (BMI) and obesity. This paper tests whether that is explained by a specific type of peer effect in obesity: genetic nurture. Specifically, we test whether an individual's weight is affected by the genes of their sibling, controlling for the individual's own genes. Using genetic data in Add Health, we find no credible evidence that an individual's BMI is affected by the polygenic risk score for BMI of their full sibling when controlling for the individual's own polygenic risk score for BMI. Thus, we find no evidence that the positive correlations in BMI between siblings are attributable to genetic nurture within families.

Estimating the effects of friends on health behaviors of adolescents

This paper estimates the effects of friends' smoking and drinking on own behavior while controlling for correlated unobservables between friends. The effect of friends' behaviors is identified by comparing similar individuals who have similar friendship opportunities and make similar friendship choices, exploiting the idea that friendship choice reveals information about unobservables. We combine this identification strategy with an across-cohort within school design so that identification arises in our reduced form estimates from across-grade differences in the clustering of health behaviors. Finally, we use estimated information on correlated unobservables to examine longitudinal data on the onset of health behaviors, where the likelihood of reverse causality should be minimal. We find evidence that this strategy produces somewhat smaller (no more than 16% smaller) friendship effect estimates than the more standard school fixed effect models consistent with at most modest bias from correlated unobservables.

Social contagion of ethnic hostility

Interethnic conflicts often escalate rapidly. Why does the behavior of masses easily change from cooperation to aggression? This paper provides an experimental test of whether ethnic hostility is contagious. Using incentivized tasks, we measured willingness to sacrifice one's own resources to harm others among adolescents from a region with a history of animosities toward the Roma people, the largest ethnic minority in Europe. To identify the influence of peers, subjects made choices after observing either destructive or peaceful behavior of peers in the same task. We found that susceptibility to follow destructive behavior more than doubled when harm was targeted against Roma rather than against coethnics. When peers were peaceful, subjects did not discriminate. We observed very similar patterns in a norms-elicitation experiment: destructive behavior toward Roma was not generally rated as more socially appropriate than when directed at coethnics, but the ratings were more sensitive to social contexts. The findings may illuminate why ethnic hostilities can spread quickly, even in societies with few visible signs of interethnic hatred.

Exploring Relationships Between Delinquent Peer Groups, Participation in Delinquency, Substance Abuse, and Injecting Drug Use Among the Incarcerated: Findings From a National Sample of State and Federal Inmates in the United States

The following study assesses the relationship between affiliating with delinquent peer groups, participation in delinquency, and several substance misuse and injecting drug use outcomes in a nationally representative sample of inmates in state and federal facilities in the United States. After controlling for potential confounders, affiliating with peers who engaged in deviant behaviors and participation in delinquency was associated with onset of alcohol and illicit drug use, substance dependence, alcohol dependence, types of substances used, and injecting drug use outcomes. Inmates who began engaging in delinquency at older ages reported initiating drug and alcohol use at older ages, and were less likely to meet the criteria for drug abuse or dependence, less likely to use substances daily or near daily, and less likely to report having ever injected or shared syringes. The implications of these findings for substance abuse, HIV, and crime prevention interventions are discussed.

Gender-specific Pathways of Peer Influence on Adolescent Suicidal Behaviors

The author explores new directions of understanding the pathways of peer influence on adolescent suicidal behavior by leveraging quasi-experimental variation in exposure to peer suicidal behaviors and tracing the flows of influence throughout school environments and networks. The author uses variation in peers' family members' suicide attempts to deploy an across-grade level, within-school analysis to estimate causal effects. Key findings include a gender-specific pathway, whereby girls are affected by their female grademates' experiences with family member suicidality but are unaffected by their male grademates. These specific pathways allow novel approaches to be used that leverage the gender specificity of the influences within an instrumental variable analysis. The findings suggest large (gender-specific) peer effects on suicidal behaviors in adolescence.

Market Conditions and Performance in the Nursing Home Compare Five-Star Rating

Previous studies have documented that market conditions affect nursing home performance; however, the evidence is inconsistent and conflicting. This study introduces three groups of county market conditions and a peer effect variable, and tests their impacts on the Nursing Home Compare (NHC) Five-Star overall rating. Indiana nursing home data and county characteristics are taken mainly from the NHC and Census Bureau websites. The result of the ordered logistic regression analysis indicates that nursing homes in excess demand markets, namely those that are highly concentrated and have fewer nursing homes, tend to perform better than their counterparts in both excess supply and balanced markets. In addition, a peer effect variable, measured as the average overall rating of the competitors, promotes performance improvement. These findings imply that small markets enable consumers to be well informed about a provider's reputation for quality, consequently enhancing performance. Furthermore, not only consumers but also providers seem to seek performance information on the report card to understand their relative position in the market, which thus affects their market strategies and subsequently performance.

Classroom Age Composition and the School Readiness of 3- and 4-Year-Olds in the Head Start Program

The federal Head Start program, designed to improve the school readiness of children from low-income families, often serves 3- and 4-year-olds in the same classrooms. Given the developmental differences between 3- and 4-year-olds, it is unknown whether educating them together in the same classrooms benefits one group, both, or neither. Using data from the Family and Child Experiences Survey 2009 cohort, this study used a peer-effects framework to examine the associations between mixed-age classrooms and the school readiness of a nationally representative sample of newly enrolled 3-year-olds (n = 1,644) and 4-year-olds (n = 1,185) in the Head Start program. Results revealed that 4-year-olds displayed fewer gains in academic skills during the preschool year when they were enrolled in classrooms with more 3-year-olds; effect sizes corresponded to 4 to 5 months of academic development. In contrast, classroom age composition was not consistently associated with 3-year-olds' school readiness.

Spillover Effects in Health Service Use: Evidence From Mental Health Care Using First-Year College Housing Assignments

Spillover effects in health service use may represent an important externality of individual treatment decisions and are important for understanding the consequences of interventions to improve access to health care. This study is the first to our knowledge to examine causal spillover effects for mental health service use. We exploit the natural experiment of first-year student housing assignments at two universities using survey data that we collected. When the peer group is defined at the roommate level, we do not find any spillover effects on service use. When the peer group is defined at the hall level, we find positive spillover effects--peers' service use increases one's own service use--and this effect is driven by individuals with prior experience with mental health services. We also find some evidence that the mechanism behind this effect is improved beliefs about treatment effectiveness.

College-Major Choice to College-Then-Major Choice

Many countries use college-major-specific admissions policies that require a student to choose a college-major pair jointly. Given the potential of student-major mismatches, we explore the equilibrium effects of postponing student choice of major. We develop a sorting equilibrium model under the college-major-specific admissions regime, allowing for match uncertainty and peer effects. We estimate the model using Chilean data. We introduce the counterfactual regime as a Stackelberg game in which a social planner chooses college-specific admissions policies and students make enrollment decisions, learn about their fits to various majors before choosing one. Our estimates indicate that switching from the baseline to the counterfactual regime leads to a 1% increase in average student welfare and that it is more likely to benefit female, low-income and/or low-ability students.

Peer effects in risk aversion

We estimate peer effects in risk attitudes in a sample of high school students. Relative risk aversion is elicited from surveys administered at school. Identification of peer effects is based on parents not being able to choose the class within the school of their choice, and on the use of instrumental variables conditional on school-grade fixed effects. We find a significant and quantitatively large impact of peers' risk attitudes on a male individual's coefficient of risk aversion. Specifically, a one standard deviation increase in the group's coefficient of risk aversion increases an individual's risk aversion by 43%. Our findings shed light on the origin and stability of risk attitudes and, more generally, on the determinants of economic preferences.

Social contagion of mental health: evidence from college roommates

From a policy standpoint, the spread of health conditions in social networks is important to quantify, because it implies externalities and possible market failures in the consumption of health interventions. Recent studies conclude that happiness and depression may be highly contagious across social ties. The results may be biased, however, because of selection and common shocks. We provide unbiased estimates by using exogenous variation from college roommate assignments. Our findings are consistent with no significant overall contagion of mental health and no more than small contagion effects for specific mental health measures, with no evidence for happiness contagion and modest evidence for anxiety and depression contagion. The weakness of the contagion effects cannot be explained by avoidance of roommates with poor mental health or by generally low social contact among roommates. We also find that similarity of baseline mental health predicts the closeness of roommate relationships, which highlights the potential for selection biases in studies of peer effects that do not have a clearly exogenous source of variation. Overall, our results suggest that mental health contagion is lower, or at least more context specific, than implied by the recent studies in the medical literature.

Peer Effects in Pro-Social Behavior: Social Norms or Social Preferences?

We compare social preference and social norm based explanations for peer effects in a three-person gift-exchange experiment. In the experiment a principal pays a wage to each of two agents, who then make effort choices sequentially. In our baseline treatment we observe that the second agent's effort is influenced by the effort choice of the first agent, even though there are no material spillovers between agents. This peer effect is predicted by the Fehr-Schmidt (1999) model of social preferences. As we show from a norms-elicitation experiment, it is also consistent with social norms compliance. A conditional logit investigation of the explanatory power of payoff inequality and elicited norms finds that the second agent's effort is best explained by the social preferences model. In further experiments we find that the peer effects change as predicted by the social preferences model. Again, a conditional logit analysis favors an explanation based on social preferences, rather than social norms. Our results suggest that, in our context, the social preferences model provides a parsimonious explanation for the observed peer effect.

Genetic sensitivity to peer behaviors: 5HTTLPR, smoking, and alcohol consumption

We investigate whether the serotonin transporter-linked polymorphic region (5HTTLPR), a gene associated with environmental sensitivity, moderates the association between smoking and drinking patterns at adolescents' schools and their corresponding risk for smoking and drinking themselves. Drawing on the school-based design of the National Longitudinal Study of Adolescent Health in conjunction with molecular genetic data for roughly 15,000 respondents (including over 2,000 sibling pairs), we show that adolescents smoke more cigarettes and consume more alcohol when attending schools with elevated rates of tobacco and alcohol use. More important, an individual's susceptibility to school-level patterns of smoking or drinking is conditional on the number of short alleles he or she has in 5HTTLPR. Overall, the findings demonstrate the utility of the differential susceptibility framework for medical sociology by suggesting that health behaviors reflect interactions between genetic factors and the prevalence of these behaviors in a person's context.

The distribution of physical activity in an after-school friendship network

OBJECTIVE

To examine whether a child's friendship network in an afterschool program influences his/her physical activity.

METHODS

Three waves of data were collected from school-aged children participating in aftercare (n = 81; mean [SD] age, 7.96 [1.74] years; 40% African American, 39% white, and 19% Latino) a name generator survey was used to map each child's social network, and accelerometers were used to measure physical activity. We applied stochastic actor-based modeling for social networks and behavior.

RESULTS

Children did not form or dissolve friendships based on physical activity levels, but existing friendships heavily influenced children's level of physical activity. The strongest influence on the amount of time children spent in moderate-to-vigorous activity in the afterschool hours was the activity level of their immediate friends. Children consistently made adjustments to their activity levels of 10% or more to emulate the activity levels of their peers (odds ratio [OR] = 6.89, P < .01). Age (OR = 0.92, P < .10) and obesity status (OR = 0.66, P < .10) had marginally significant and relatively small direct effects on the activity. Gender had no direct effect on activity.

CONCLUSIONS

These results suggest that friendship ties play a critical role in setting physical activity patterns in children as young as 5 to 12 years. Children's activity levels can be increased, decreased, or stabilized depending on the activity level of their immediate social network during a 12-week afterschool program. Network-based interventions hold the potential to produce clinically significant changes to children's physical activity.

Peer effects in learning HIV results

How do neighbors positively or negatively influence individuals living in rural Malawi to learn their HIV results? Using data of location of homes and distance to neighbors, we measure the social network effects of neighbors' learning their HIV results on individuals own learning. Using the fact that neighbors were randomly offered monetary incentives of varying amounts to learn their HIV results, we find positive effects of neighbors attending clinics on others living nearby: a 10 percentage point increase of the percentage of neighbors (approximately 2.4 individuals) learning their HIV results increases the probability of learning HIV results by 1.1 percentage points. The strongest network effects are among closest neighbors; we find no effect among religious social networks. We also find a negative interaction between direct cash incentives and peers: the effect of peers doubles among those who were not offered any individual financial incentive to learn their HIV results.

All in the Family: Mental Health Spillover Effects between Working Spouses

It is well documented that mental health outcomes are correlated between spouses. There are several alternative hypotheses for this correlation, including both causal and non-causal pathways. In this paper, I use an instrumental variables/fixed effects approach to examine whether there is evidence that an individual's mental health status spills over on his or her spouse's mental health status. Results from the IV-FE specifications that use spousal job problems as an instrument are large in magnitude. In particular, spousal mental health status is estimated to have a greater influence on an individual's mental health status than his or her own mental health endowment and is similar in magnitude with his or her own physical health status. Although not conclusive, these findings suggest that within-family spillovers of mental illness could be economically important and that policies that reduce mental health problems for individuals likely have unmeasured benefits for their family members.

Improving Education in the Developing World: What Have We Learned from Randomized Evaluations?

Across a range of contexts, reductions in education costs and provision of subsidies can boost school participation, often dramatically. Decisions to attend school seem subject to peer effects and time-inconsistent preferences. Merit scholarships, school health programs, and information about returns to education can all cost-effectively spur school participation. However, distortions in education systems, such as weak teacher incentives and elite-oriented curricula, undermine learning in school and much of the impact of increasing existing educational spending. Pedagogical innovations designed to address these distortions (such as technology-assisted instruction, remedial education, and tracking by achievement) can raise test scores at a low cost. Merely informing parents about school conditions seems insufficient to improve teacher incentives, and evidence on merit pay is mixed, but hiring teachers locally on short-term contracts can save money and improve educational outcomes. School vouchers can cost-effectively increase both school participation and learning.