Dissertation Defense: “Essays in Human Capital Formation”, Nicolas Fuertes Segura, University of California, Santa Barbara

Speaker

Nicolas Fuertes Segura, University of California, Santa Barbara

Biography

Nicolás Fuertes-Segura is a Ph.D. Candidate in Economics at the University of California, Santa Barbara. His research focuses on Labor and Health economics with a primary interest in peer and network effects. Nicolás' research has been honored with the 2025 ASHEcon “Health and Development” Program Chair Award.

His recent work examines how friendships are formed and persist over time, as well as the impact of these friendships on both cognitive and non-cognitive skills. This paper finds that the timing and length of classroom exposure, as well as homophily, affect the formation and persistence of friendships. Regarding cognitive and non cognitive skill, the paper finds that friendship networks positively affect math and executive function and reduce the symptoms of depression. These findings are significant as they highlight the importance of accounting for peer composition and homophily when evaluating how friendships form and persist and how classroom environments affect cognitive development.

Prior to joining UCSB, Nicolás worked at the Office of the Manager of the Social Sector at the Inter-American
Development Bank in Washington D.C. where he conducted research on labor markets and economics of education. He was also the Data Center Coordinator at the School of Economics of the Universidad de los Andes in Bogotá, Colombia.

Title

“Essays in Human Capital Formation”

Abstract

This dissertation examines how social environments and early-life shocks shape cognitive, socioemotional, and behavioral outcomes in developing countries. Across three chapters, I combine experimental data, panel data, survey data, and quasi-experimental methods.

The first chapter, coauthored with Yyannú Cruz-Aguayo, studies the causal impact of friendships on children's
outcomes in elementary schools in Ecuador. While the literature on peer effects typically focuses on broad measures of peer composition, such as average ability or class characteristics, friendships represent a more direct and behaviorally relevant form of interaction. Furthermore, little is known about whether friendships help or hurt learning and well-being. Friendships can provide emotional support and foster motivation, but they may also distract from academic activities or reinforce negative behaviors. We use a unique randomized experiment in which students are randomly assigned to classrooms in every grade from Kindergarten to 6th grade, combined with detailed network data. We show that being assigned to a classroom with more friends has contrasting effects across domains: it reduces cognitive outcomes, such as math and executive function, while improving emotional well-being. These findings highlight that friendships hurt academic performance but improve socioemotional outcomes. We further show that these negative effects are driven by the number of disruptive friends and are concentrated among male students. Overall, these findings suggest that friendship networks may affect learning through a distraction or lack of attention channel.

The second chapter, coauthored with Yyannú Cruz-Aguayo and Carolina Echeverri, examines how exposure to high achievers in the classroom affects cognitive and non-cognitive skills. Using the same experimental setting, we exploit random variation in the proportion of high achievers across classrooms. We find that exposure to high achievers reduces math and executive function scores, with stronger effects among top-performing students. The results suggest that heightened competition, greater peer interaction, and increased salience of relative class rank play an important role in shaping outcomes. In addition, we show that higher-quality teachers can mitigate these negative effects, highlighting the interaction between peer composition and classroom management.

The third chapter studies the impact of exposure to violence during childhood (0-9 years old) on socioemotional skills and risky health behaviors in adolescence. Using data from the Colombian Longitudinal Survey and municipality-level administrative data, and exploiting within-municipality variation across cohorts in exposure to terrorist attacks during childhood, I estimate the effects of violence on adolescent outcomes. The results show that exposure to conflict affects socioemotional development and increases engagement in risky behaviors, particularly drinking alcohol. These findings contribute to the literature on the potential long-term consequences of violence and highlight the importance of early-life conditions in shaping behavioral and health outcomes during adolescence.

JEL Codes: I21, J16, I12, J13, D85, Z13, D10, F51

Event Details

Join us for Nicolas’s dissertation defense, where he will present his research titled “Essays in Human Capital
Formation” We invite you to attend this important academic milestone and learn more about her work in the field. To access a copy of the dissertation here, you must have an active UCSB NetID and password.