This note's aim is to investigate the sensitivity of Christakis and Fowler's claim [Christakis, N., Fowler, J., 2007. The spread of obesity in a large social network over 32 years. The New England Journal of Medicine 357, 370-379] that obesity has spread through social networks. It is well known in the economics literature that failure to include contextual effects can lead to spurious inference on "social network effects." We replicate the NEJM results using their specification and a complementary dataset. We find that point estimates of the "social network effect" are reduced and become statistically indistinguishable from zero once standard econometric techniques are implemented. We further note the presence of estimation bias resulting from use of an incorrectly specified dynamic model.

SignificanceGenome-wide association study (GWAS) discoveries about educational attainment have raised questions about the meaning of the genetics of success. These discoveries could offer clues about biological mechanisms or, because children inherit genetics and social class from parents, education-linked genetics could be spurious correlates of socially transmitted advantages. To distinguish between these hypotheses, we studied social mobility in five cohorts from three countries. We found that people with more education-linked genetics were more successful compared with parents and siblings. We also found mothers’ education-linked genetics predicted their children’s attainment over and above the children’s own genetics, indicating an environmentally mediated genetic effect. Findings reject pure social-transmission explanations of education GWAS discoveries. Instead, genetics influences attainment directly through social mobility and indirectly through family environments.

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This paper contributes to the literature on the relationship between adolescent depression and educational attainment in several ways. First, while cross-sectional data are normally used, this paper uses longitudinal data in order to defend against the potential of reverse causality. Second, this is the first paper in the literature to control for sibling-fixed effects in examining the relationship between adolescent depressive symptoms and human capital accumulation. Importantly, this eliminates omitted factors such as family and neighborhood characteristics common to siblings that affect both depressive symptoms and educational attainments (e.g. neighborhood crime, and family resources). Third, this paper examines the effects of both an indicator and scale of depressive symptoms and finds important associations with these depressive symptoms and human capital accumulation. Though the results cannot be given a causal interpretation, the findings show a negative relationship between depressive symptoms and years of schooling. The relationship appears to be driven primarily through increasing the chances of dropping out but may have small impacts on the likelihood of college attendance (conditional on high school graduation). In particular, preferred estimates suggest that a standard deviation increase in depressive symptoms is associated with a 25-30% increase in the likelihood of dropping out.

U nderstanding the influence of school composition on individual outcomes is central to the evaluation of many education policies including efforts to desegregate schools, single sex schooling, expanded school choice, and policies to assimilate immigrant students. Much of the research on school composition, however, has focused on a narrow range of short-term outcomes, limiting our understanding of these effects. This study applies recently developed methods for identifying the causal effect of peers using the National Longitudinal Study of Adolescent Health This paper uses a within-school/across-cohort design to present new evidence of the effects of high school classmate characteristics on a wide range of post-secondary outcomes. We find that increases in the percent of classmates with college-educated mothers decreases the likelihood of dropping out and increases the likelihood of attending college, despite showing no impact on a range of in-school achievement, attitudes, and behaviors. The percent of students from disadvantaged minority groups does not show any effects on postsecondary outcomes, but is associated with students reporting less caring student-teacher relationships and increased prevalence of some undesirable student behaviors during high school. (JEL I21, J13, J15)