We develop a Roy model of social interactions in which individuals sort into peer groups based on comparative advantage. Two key results emerge: First, when comparative advantage is the guiding principle of peer group organization, the effect of moving a student into an environment with...

We take cohorts of entering freshmen at the United States Air Force Academy and assign half to peer groups with the goal of maximizing the academic performance of the lowest ability students. Our assignment algorithm uses peer effects estimates from the observational data. We find a negative and...

Using exogenous secondary school assignments to remove self-selection bias to schools and peers within schools, I credibly estimate both (1) the effect of attending schools with higher-achieving peers, and (2) the direct effect of short-run peer quality improvements within schools, on the same...

This paper estimates treatment size and status specific peer effects that are not detected by widely-used approaches to the estimation of spillovers. In a field experiment using university students, we find that subjects who have been incentivized to exercise increase gym usage more if they have...

The increase in obesity over the past thirty years has led researchers to investigate the role of social networks as a contributing factor. However, several challenges make it difficult to demonstrate a causal link between friends' physical fitness and own fitness using observational data. To...

Reinforcing earlier findings from other data, college senior fraternity/sorority members are more likely to consume alcohol frequently. Large reductions in estimates upon controlling for time spent partying, and to a lesser extent cigarette use and intramural sports involvement, suggest...

Detailed administrative data from a large and diverse community college are used to examine if academic performance depends on whether students are the same race or ethnicity as their instructors. To identify racial interactions and address many threats to internal validity we estimate models...

We conducted a field experiment in a 401(k) plan to measure the effect of disseminating information about peer behavior on savings. Low-saving employees received simplified plan enrollment or contribution increase forms. A randomized subset of forms stated the fraction of age-matched coworkers...

We study social interactions in the risky behavior of best-friend pairs in the National Longitudinal Study of Adolescent Health (Add Health). Focusing on friends who had not yet initiated a particular behavior (sex, smoking, marijuana use, truancy) by the first wave of the survey, we estimate...

This paper compares two methods to encourage socially optimal provision of a public good. We compare the efficacy of vigilante justice, as represented by peer-to-peer punishment, to delegated policing, as represented by the "hired gun" mechanism, to deter free riding and improve group welfare....