Learning from Neighbors about a Changing State

Agents learn about a changing state using private signals and past actions of neighbors in a network. We characterize equilibrium learning and social influence in this setting. We then examine when agents can aggregate information well, responding quickly to recent changes. A key sufficient condition for good aggregation is that each individual's neighbors have sufficiently different types of private information. In contrast, when signals are homogeneous, aggregation is suboptimal on any network. We also examine behavioral versions of the model, and show that achieving good aggregation requires a sophisticated understanding of correlations in neighbors' actions. The model provides a Bayesian foundation for a tractable learning dynamic in networks, closely related to the DeGroot model, and offers new tools for counterfactual and welfare analyses.Comment: minor revision tweaking exposition relative to v5 - which added new Section 3.2.2, new Theorem 2, new Section 7.1, many local revision

Naïve Learning in Social Networks: Convergence, Influence and Wisdom of Crowds

We study learning and influence in a setting where agents communicate according to an arbitrary social network and naïvely update their beliefs by repeatedly taking weighted averages of their neighbors’ opinions. A focus is on conditions under which beliefs of all agents in large societies converge to the truth, despite their naïve updating. We show that this happens if and only if the influence of the most influential agent in the society is vanishing as the society grows. Using simple examples, we identify two main obstructions which can prevent this. By ruling out these obstructions, we provide general structural conditions on the social network that are sufficient for convergence to truth. In addition, we show how social influence changes when some agents redistribute their trust, and we provide a complete characterization of the social networks for which there is a convergence of beliefs. Finally, we survey some recent structural results on the speed of convergence and relate these to issues of segregation, polarization and propaganda.Social Networks, Learning, Diffusion, Bounded Rationality

How Homophily Affects Learning and Diffusion in Networks

We examine how three different communication processes operating through social networks are affected by homophily - the tendency of individuals to associate with others similar to themselves. Homophily has no effect if messages are broadcast or sent via shortest paths; only connection density matters. In contrast, homophily substantially slows learning based on repeated averaging of neighbors' information and Markovian diffusion processes such as the Google random surfer model. Indeed, the latter processes are strongly affected by homophily but completely independent of connection density, provided this density exceeds a low threshold. We obtain these results by establishing new results on the spectra of large random graphs and relating the spectra to homophily. We conclude by checking the theoretical predictions using observed high school friendship networks from the Adolescent Health dataset.Networks, Learning, Diffusion, Homophily, Friendships, Social Networks, Random Graphs, Mixing Time, Convergence, Speed of Learning, Speed of Convergence

Informality, Trade Policies And Smuggling In West Africa

In West Africa, recorded intra-regional trade is small but informal cross-border trade (ICBT) is pervasive, despite regional integration schemes intended to promote official trade. We argue that ICBT must be understood in light of two features of West African national boundaries: divergent economic policies between neighboring countries and the ease with which informal operators can ship goods across borders. We focus on two ICBT clusters: Senegal–The Gambia and Nigeria–Benin–Togo. Nigeria and Senegal have protected their domestic industries with high import barriers, whereas Benin, Togo and The Gambia have maintained lower import taxation. These differential trade policies, together with high mobility of goods and people across borders, lead to widespread smuggling, with goods imported legally in low-tax countries and re-exported unofficially to countries with higher import duties

Into the blackboard jungle: educational debate and cultural change in 1950s America

textThis dissertation examines the moral panic over America's education "crisis" in the 1950s. Unlike traditional histories of postwar education, which tend to focus on curricular debates, institutional change, and major events like Sputnik and Little Rock, this interdisciplinary project turns its attention to popular culture. It analyzes everyday depictions of the school crisis that appeared in newspapers, magazines, films, and bestselling books, and discusses these depictions in terms of cultural production and audience reception. Specifically, it explores the ways in which popular culture shaped educational debates and influenced school reform efforts in the fifties. In the final analysis, it also shows how the public school was transformed into a symbol of fear and danger in postwar American culture. My dissertation argues that the democratization of education after World War II, which was spurred by rising enrollments, desegregation, and the G.I. Bill, simultaneously engendered cultural anxieties about the prospect of achieving educational and social equality in the fifties. As public schools grew more diverse along lines of race, class, gender, age, and ability level, they grew more dangerous in the popular imagination. Chapter one traces the origins of the education panic, while chapters two through four discuss three popular narratives about the school crisis. Chapter two offers a case study of a local school crisis in Pasadena, California that attracted national attention in the early fifties; it reads the history of Pasadena's educational conflict as an outgrowth of urban migration, McCarthyism, and the backlash against progressive education. Chapter three explains how both the novel and film versions of The Blackboard Jungle, which focused on racially diverse, blue-collar high school students, significantly influenced public discourse about America’s "dangerous" schools at mid-decade. Chapter four studies popular depictions of the back-to-basics movement—a self-proclaimed antidote to the school crisis—and considers the movement’s rhetorical appeals alongside social anxieties about masculinity, conformity, and rapid cultural change. Chapter five outlines the legacies of the postwar education crisis, demonstrating the ways in which the rhetoric of fear and schooling that was forged in the fifties continues to influence popular debates about public education today.American Studie

Games on Endogenous Networks

We study network games in which players both create spillovers for one another and choose with whom to associate. The endogenous outcomes include both the strategic actions (e.g., effort levels) and the network in which spillovers occur. We introduce a framework and two solution concepts that extend standard approaches -- Nash equilibrium in actions and pairwise (Nash) stability in links. Our main results show that under suitable monotonicity assumptions on incentives, stable networks take simple forms. Our central conditions concern whether actions and links are strategic complements or substitutes, as well as whether links create positive or negative payoff spillovers. We apply our model to understand the consequences of competition for status, to microfound matching models that assume clique formation, and to interpret empirical findings that highlight unintended consequences of group design