Martin Koenen

Hello!

I am a PhD Candidate in Political Economy and Government at Harvard, and a research affiliate at Opportunity Insights and the Institute for Quantitative Social Science.

In my research, I primarily explore how social capital shapes economic outcomes, for instance by influencing where people live and how much they earn. In a second strand of work, I investigate the causes and consequences of political preferences and polarization.

Before graduate school, I worked at Opportunity Insights and earned a MSc in Economics from the University of Mannheim, and a BSc in Economics from Humboldt University of Berlin.

I am currently on the 2024-2025 economics job market.

Job Market Paper

Social Ties and Residential Choice: Micro Evidence and Equilibrium Implications

with Drew Johnston

Abstract

Why don't more people move to places where they can earn higher incomes? We use individual-level data from Facebook to find that social ties play a crucial role in explaining this puzzle: social ties are concentrated locally and shape migration decisions. On average, individuals live within 100 miles of nearly 80% of their friends, with less-educated individuals having even more concentrated social networks. To establish a causal link between the location of one's friends and migration, we exploit plausibly exogenous variation in the timing of friends' moves around individuals' college graduation. Having one more friend in a given commuting zone at the time of graduation increases one's likelihood of living there by 0.3 percentage points, which is comparable in magnitude to the effect of a $470 increase in annual wages. We incorporate these findings into a spatial equilibrium model and show that the magnitude of social network effects can explain why people stay in poorer places and why less-educated people are much less responsive to economic shocks. Overall, this study shows that social networks play a first-order role --- as important or more important than canonical economic factors such as wages and rents --- in determining residential choice at the individual and aggregate level.

Working Papers

Political Sorting in the U.S. Labor Market: Evidence and Explanations

with Sahil Chinoy

Abstract

We study political sorting in the labor market and examine its sources. Merging voter file data and online résumés to create a panel of 34.5 million people, we show that Democrats and Republicans choose distinctive career paths and employers. This leads to marked segregation at the workplace: a Democrat or Republican's coworker is 10% more likely to share their party than expected. Then, we ask whether segregation arises because jobs shape workers' politics or because workers' politics shape their job choices. To study the first, we use a quasi-experimental design leveraging the timing of job transitions. We find that uncommitted workers do adopt the politics of their workplace, but not workers who were already registered Democrats or Republicans. The average effect is too small to generate the segregation we document. To study the second, we measure the intensity of workers' preferences for politically compatible jobs using two survey experiments motivated by the observational data. Here, we find that the median Democrat or Republican would trade off 3% in annual wages for an ideologically congruent version of a similar job. These preferences are strong enough to generate segregation similar to the observed levels.

The Effect of Childhood Environment on Political Behavior: Evidence From Young U.S. Movers, 1992-2021

with Jacob Brown, Enrico Cantoni, Sahil Chinoy and Vincent Pons

Abstract

We ask how childhood environment shapes political behavior. We measure young voters’ participation and party affiliation in nationally comprehensive voter files and reconstruct their childhood location histories based on their parents’ addresses. We compare outcomes of individuals who moved between the same origin and destination counties but at different ages. Those who spend more time in the destination are more influenced by it: Growing up in a county where their peers are 10 percentage points more likely to become Republicans makes them 4.7 percentage points more likely to become Republican themselves upon entering the electorate. The effects are of similar magnitude for Democratic partisanship and turnout. These exposure effects are primarily driven by teenage years, and they persist but decay after the first election. They reflect both state-level factors and factors varying at a smaller scale such as peer effects.

The Social Integration of International Migrants: Evidence from the Networks of Syrians in Germany

with Michael Bailey, Drew Johnston, Theresa Kuchler, Dominic Russel, and Johannes Stroebel
Conditionally Accepted at the Journal of Political Economy
Research Summary | Research Summary (German version) | Slides | Poster (winner, Best Poster at IC2S2 '22)

Abstract

We use de-identified friendship data from Facebook to study the social integration of Syrian migrants in Germany. We decompose the significant spatial variation in migrants’ integration levels into the rate at which Germans befriend their neighbors in general and the particular rate at which they befriend Syrian migrants versus other Germans. We follow the friending behavior of Germans that move across locations to show that both forces are more affected by local institutions and policies than persistent individual characteristics or preferences of local natives. We explore the characteristics of places with higher integration levels, and show that integration courses causally affect place-specific equilibrium integration levels by shifting the rates of Germans befriending Syrians.

Does Contact Reduce Affective Polarization? Field Evidence from Germany

with Adrian Blattner

Abstract

We analyze whether and how exposure to political opponents can impact attitudes towards political opponents (affective polarization) and extremity of political opinions (ideological polarization). We present findings from a quasi-experiment in Germany that matched 15,000 participants for a virtual one-on-one conversation with a stranger. Leveraging staggered treatment assignment, we find significant reductions in affective polarization among treated participants in both incentivized economic interactions and survey outcomes. The reductions are concentrated among participants who are more polarized and less interested in conversations at baseline. In contrast, we do not find corresponding effects on ideological polarization suggesting that exposure increases tolerance but not support for opposing positions. In ongoing work, we are extending the analysis to a series of field experiments in Brazil and the U.S. to study factors that drive demand for contact and mechanisms explaining under which conditions contact leads to durable reductions in animosity.

Published Research

Social Networks Shape Beliefs and Behavior: Evidence from Social Distancing during the COVID-19 Pandemic

with Michael Bailey, Drew Johnston, Theresa Kuchler, Dominic Russel, and Johannes Stroebel
Journal of Political Economy Microeconomics, 2 (3), 463-494, August 2024
Press: NBER Digest
Appendix | Slides | Code | WP Version

Abstract

We analyze de-identified data from Facebook to show how social connections affect beliefs and behaviors in high-stakes settings. During the Covid-19 pandemic, individuals with friends in regions facing severe disease outbreaks reduced their mobility more than their demographically similar neighbors with friends in less affected areas. To explore why social connections shape behaviors, we show that individuals with higher friend exposure to Covid-19 are more supportive of social distancing measures and less likely to advocate to reopen the economy. We conclude that friends influence individuals’ behaviors in part through their beliefs, even when there is abundant information from expert sources.

Social Capital I: Measurement and Associations with Economic Mobility

Abstract

Social capital—the strength of an individual’s social network and community—has been identified as a potential determinant of outcomes ranging from education to health. However, efforts to understand what types of social capital matter for these outcomes have been hindered by a lack of social network data. Here, in the first of a pair of papers9, we use data on 21 billion friendships from Facebook to study social capital. We measure and analyse three types of social capital by ZIP (postal) code in the United States: (1) connectedness between different types of people, such as those with low versus high socioeconomic status (SES); (2) social cohesion, such as the extent of cliques in friendship networks; and (3) civic engagement, such as rates of volunteering. These measures vary substantially across areas, but are not highly correlated with each other. We demonstrate the importance of distinguishing these forms of social capital by analysing their associations with economic mobility across areas. The share of high-SES friends among individuals with low SES—which we term economic connectedness—is among the strongest predictors of upward income mobility identified to date. Other social capital measures are not strongly associated with economic mobility. If children with low-SES parents were to grow up in counties with economic connectedness comparable to that of the average child with high-SES parents, their incomes in adulthood would increase by 20% on average. Differences in economic connectedness can explain well-known relationships between upward income mobility and racial segregation, poverty rates, and inequality. To support further research and policy interventions, we publicly release privacy-protected statistics on social capital by ZIP code at https://www.socialcapital.org

Social Capital II: Determinants of Economic Connectedness

Abstract

Low levels of social interaction across class lines have generated widespread concern and are associated with worse outcomes, such as lower rates of upward income mobility. Here we analyse the determinants of cross-class interaction using data from Facebook, building on the analysis in our companion paper. We show that about half of the social disconnection across socioeconomic lines—measured as the difference in the share of high-socioeconomic status (SES) friends between people with low and high SES—is explained by differences in exposure to people with high SES in groups such as schools and religious organizations. The other half is explained by friending bias—the tendency for people with low SES to befriend people with high SES at lower rates even conditional on exposure. Friending bias is shaped by the structure of the groups in which people interact. For example, friending bias is higher in larger and more diverse groups and lower in religious organizations than in schools and workplaces. Distinguishing exposure from friending bias is helpful for identifying interventions to increase cross-SES friendships (economic connectedness). Using fluctuations in the share of students with high SES across high school cohorts, we show that increases in high-SES exposure lead low-SES people to form more friendships with high-SES people in schools that exhibit low levels of friending bias. Thus, socioeconomic integration can increase economic connectedness in communities in which friending bias is low. By contrast, when friending bias is high, increasing cross-SES interactions among existing members may be necessary to increase economic connectedness. To support such efforts, we release privacy-protected statistics on economic connectedness, exposure and friending bias for each ZIP (postal) code, high school and college in the United States at https://www.socialcapital.org.