Published Papers

This paper uses social networks to identify information transfer in security markets. We focus on connections between mutual fund managers and corporate board members via shared education networks. We find that portfolio managers place larger bets on connected firms and perform significantly better on these holdings relative to their nonconnected holdings. A replicating portfolio of connected stocks outperforms nonconnected stocks by up to 7.8 percent per year. Returns are concentrated around corporate news announcements, consistent with portfolio managers gaining an informational advantage through the education networks. Our results suggest that social networks may be important mechanisms for information flow into asset prices.

Using a novel data set of U.S. financial advisors that includes individuals' employment histories and misconduct records, we show that coworkers influence an individual's propensity to commit financial misconduct. We identify coworkers' effect on misconduct using changes in coworkers caused by mergers of financial advisory firms. The tests include merger-firm fixed effects to exploit the variation in changes to coworkers across branches of the same firm. The probability of an advisor committing misconduct increases if his new coworkers, encountered in the merger, have a history of misconduct. This effect is stronger between demographically similar coworkers.

The prevalence of shirking within a large Italian bank appears to be characterized by significant regional differentials. In particular, absenteeism and misconduct episodes are substantially more prevalent in the south. We consider a number of potential explanations for this fact: different individual backgrounds; group-interaction effects; sorting of workers across regions; differences in local attributes; different hiring policies; and discrimination against southern workers. Our analysis suggests that individual backgrounds, group-interaction effects, and sorting effects contribute to explaining the north-south shirking differential. None of the other explanations appears to be of first-order importance.

We study subjects who were asked to fill letters into envelopes with a remuneration independent of output. In the "pair" treatment, two subjects worked at the same time in the same room, and peer effects were possible. In the "single" treatment, subjects worked alone, and peer effects were ruled out. We find evidence of peer effects in the pair treatment because the standard deviations of output are smaller within pairs than between pairs. Moreover, average output is higher in the pair treatment: thus, peer effects raise productivity. Finally, low-productivity workers are the most sensitive to the behavior of peers.

I investigate the effect of faculty quality on PhD student outcomes. To address the endogeneity of faculty quality I use exogenous variation provided by the expulsion of mathematics professors in Nazi Germany. Faculty quality is a very important determinant of short- and long-run PhD student outcomes. A one-standard-deviation increase in faculty quality increases the probability of publishing the dissertation in a top journal by 13 percentage points, the probability of becoming a full professor by 10 percentage points, the probability of having positive lifetime citations by 16 percentage points, and the number of lifetime citations by 6.3.

We present evidence on the effect of social connections between workers and managers on productivity in the workplace. To evaluate whether the existence of social connections is beneficial to the firm's overall performance, we explore how the effects of social connections vary with the strength of managerial incentives and worker's ability. To do so, we combine panel data on individual worker's productivity from personnel records with a natural field experiment in which we engineered an exogenous change in managerial incentives, from fixed wages to bonuses based on the average productivity of the workers managed. We find that when managers are paid fixed wages, they favor workers to whom they are socially connected irrespective of the worker's ability, but when they are paid performance bonuses, they target their effort toward high ability workers irrespective of whether they are socially connected to them or not. Although social connections increase the performance of connected workers, we find that favoring connected workers is detrimental for the firm's overall performance.

We study peer effects in the workplace. Specifically, we investigate whether, how, and why the productivity of a worker depends on the productivity of coworkers in the same team. Using high-frequency data on worker productivity from a large supermarket chain, we find strong evidence of positive productivity spillovers from the introduction of highly productive personnel into a shift. Worker effort is positively related to the productivity of workers who see him, but not workers who do not see him. Additionally, workers respond more to the presence of coworkers with whom they frequently interact. We conclude that social pressure can partially internalize free-riding externalities that are built into many workplaces.

In this paper, we bring together and advance a growing literature on a third feature: worker self-control. Individuals may not be able to work as hard as they would like. Some workplace arrangements may make self-control problems more severe, while others may ameliorate them.Below, we describe evidence from a field experiment broadly supportive of the selfcontrol perspective. We then argue that many work arrangements can be understood differently through this perspective. Specifically, we use self-control considerations to interpret the productivity increases and changes in work organization that accompany the shift from agrarian to industrialized production.

We study how peers impact worker productivity growth among salespeople in the cosmetics department of a department store. We first exploit a shift assignment policy that creates exogenous variation in salespersons' peers each week to identify and quantify sources of worker learning. We find that peer-based learning is more important than learning-by-doing for individuals, and there is no evidence of forgetting. Working with high-ability peers substantially increases the long-term productivity growth of new salespeople. We then examine possible mechanisms behind peer-based learning by exploiting the multiple colocated firms in our setting that sell products with different task difficulties and compensate their sales forces using either team-based or individual-based compensation systems. The variation in incentives to compete and cooperate within and across firm boundaries, combined with variation in sales difficulty for different product classes, allows us to suggest two mechanisms behind peer-based learning: observing successful sales techniques of peers and direct teaching. Our paper advocates the importance of learning from one another in the workplace and suggests that individual peer-based learning is a foundation of both organizational learning curves and knowledge spillovers across firms.

We estimate the magnitude of spillovers generated by 112 academic "superstars" who died prematurely and unexpectedly, thus providing an exogenous source of variation in the structure of their collaborators' coauthorship networks. Following the death of a superstar, we find that collaborators experience, on average, a lasting 5% to 8% decline in their quality-adjusted publication rates. By exploring interactions of the treatment effect with a variety of star, coauthor, and star/coauthor characteristics, we seek to adjudicate between plausible mechanisms that might explain this finding. Taken together, our results suggest that spillovers are circumscribed in idea space, but less so in physical or social space. In particular, superstar extinction reveals the boundaries of the scientific field to which the star contributes-the "invisible college".

Using longitudinal elementary school teacher and student data, we document that students have larger test score gains when their teachers experience improvements in the observable characteristics of their colleagues. Using within-school and within-teacher variation, we show that a teacher's students have larger achievement gains in math and reading when she has more effective colleagues (based on estimated value-added from an out-of-sample pre-period). Spillovers are strongest for less experienced teachers and persist over time, and historical peer quality explains away about 20 percent of the own-teacher effect, results that suggest peer learning.

This paper examines the informational role of product ratings. We build a theoretical model in which ratings can help consumers figure out how much they would enjoy the product. In our model, a high average rating indicates a high product quality, whereas a high variance of ratings is associated with a niche product, one that some consumers love and others hate. Based on its informational role, a higher variance would correspond to a higher subsequent demand if and only if the average rating is low. We find empirical evidence that is consistent with the theoretical predictions with book data from Amazon.com and BN.com. A higher standard deviation of ratings on Amazon improves a book's relative sales rank when the average rating is lower than 4.1 stars, which is true for 35% of all the books in our sample.