Working papers

Security Transitions, with Thiemo Fetzer (Warwick), Oliver Vanden Eynde (PSE) and Austin Wright (Chicago)

Conditionally accepted at the American Economic Review

How do foreign powers disengage from a conflict? We study the recent large- scale security transition from international troops to local forces in the context of the ongoing civil conflict in Afghanistan. We construct a new dataset that com- bines information on this transition process with declassified conflict outcomes and previously unreleased quarterly survey data. Our empirical design leverages the staggered roll-out of the transition onset, together with a novel instrumental variables approach to estimate the impact of the two-phase security transition. We find that the initial security transfer to Afghan forces is marked by a significant, sharp and timely decline in insurgent violence. This effect reverses with the ac- tual physical withdrawal of foreign troops. We argue that this pattern is consistent with a signaling model, in which the insurgents reduce violence strategically to facilitate the foreign military withdrawal. Our findings clarify the destabilizing consequences of withdrawal in one of the costliest conflicts in modern history and yield potentially actionable insights for designing future security transitions.

Identifying Network Ties from Panel Data: Theory and an Application to Tax Competition, with Aureo de Paula and Imran Rasul (UCL), 2019

Revise and Resubmit at the Review of Economic Studies


We present results on the identification of social networks from observational panel data that contains no information on social ties between agents. In the context of a canonical social interactions model, we provide sufficient conditions under which the social interactions matrix, endogenous and exogenous social effect parameters are all globally identified. While this result is relevant across different estimation strategies, we then describe how high-dimensional estimation techniques can be used to estimate the interactions model based on the Adaptive Elastic Net GMM method. We employ the method to study tax competition across US states. We find the identified social interactions matrix implies tax competition differs markedly from the common assumption of competition between geographically neighboring states, providing further insights for the long-standing debate on the relative roles of factor mobility and yardstick competition in driving tax setting behavior across states. Most broadly, our identification and application show the analysis of social interactions can be extended to economic realms where no network data exists.

Housing Insecurity, Homelessness and Populism: Evidence from the UK, with Thiemo Fetzer and Srinjoy Sen (Warwick), 2019



Media coverage: Economist, VoxEU

Homelessness and precarious living conditions are on the rise across much of the Western world. This paper exploits quasi-exogenous variation in the affordability of rents due to a cut to rent subsidies for low income benefit in the United Kingdom in April 2011. Using individual-level panel data as mo- tivating evidence, we document that individuals exposed to the cut were significantly more likely to build up rent arrears and face evictions; further, they were more likely to endogenously attrit from the panel. Using comprehensive district-level administrative data, we show that the affordability shock caused a significant increase in: evictions; individual bankruptcies; property crimes; insecure temporary housing arrangements; statutory homelessness and actual rough sleeping with most notable rise in statutory homelessness among fam- ilies with children. We also note political effects: the cut reduces electoral registration rates, and is associated with lower turnout and higher support for Leave in the 2016 EU referendum, likely capturing a change in composition of those that engage with democratic processes. Lastly, we estimate that the fiscal savings were much lower than anticipated: for every pound saved by the central government, council spending to meet statutory obligations for home- lessness prevention increased by 53 pence, rendering the cost savings much smaller than expected.

Searching for Answers: the Impact of Student Access to Wikipedia, with Laura Derksen and Catherine Michaud Leclerc (Toronto), 2019



Young people across the developing world are gaining access to the internet. Can schools introduce the internet in a way that promotes reading and learning? We provide Wikipedia access to a random subset of secondary school students in Malawian boarding schools. This setting is unique: students otherwise have limited study resources and no internet access. Students used Wikipedia intensively, and found it accessible and trustworthy. They developed a preference for Wikipedia over other online sources, including for information about news events and safe sex. We find a large impact on English final exam scores (.11 standard deviations), especially for low achievers (.21 standard deviations). Students also used Wikipedia to study for Biology, and exam scores increased for low achievers (.17 standard deviations). Our results imply that Wikipedia is a source of simple and engaging reading material, and can improve English language skills. It is also a source of accessible study material that increases study time productivity for low achievers

Does Community Policing Build Trust in Police and Reduce Crime? Evidence from Six Coordinated Field Experiments in the Global South, part of Metaketa IV initiative


Part of Metaketa IV initiative

Is it possible for societies to reduce crime without creating or exacerbating adversarial relationships between the police and citizens? Community- oriented policing is a widely celebrated reform that aims to do so, and advocates are calling for its adoption around the world. However, the evidence base is limited to a small number of countries, does not generally study the bundle of practices commonly implemented together, and is largely silent on effects on trust. We designed six field experiments with police agencies in the Global South to study locally-designed models of community policing, with coordinated measures of crime and the attitudes and behaviors of citizens and police from both surveys and administrative data. In a preregistered meta-analysis, we find that these interventions largely failed to improve citizen-police relations and do not reduce crime. In these contexts, structural reforms to police agencies may be required for incremental reforms modeled on community policing to succeed.

Internet Access, Social Media and the Behavior of Politicians: Evidence from Brazil, with P Bessone (MIT), F Campante (John Hopkins), and C Ferraz (UBC) 

Link: [updated paper soon]

Recent years have witnessed the remarkable diffusion of social media in tandem with the spread of mobile phones that are, in many places, the key tool for accessing those media. We ask whether this has affected the communication and responsiveness of politicians to- wards voters. Using data on the spread of the 3G mobile phone network in Brazil, and self- collected data on the universe of Facebook activities by federal legislators, we examine how legislators respond when municipalities that are part of their electoral base obtain access to the 3G technology. We find that politicians increase their online engagement with vot- ers that gain 3G mobile access but decrease their offline engagement measured by speeches and earmarked transfers towards connected localities where they have a large pre-existing vote share. Our results suggests that instead of increasing responsiveness, social media may enable politicians to solidify their position with core supporters using communication strategies while shifting resources away towards localities that lack 3G internet access.


Losing on the Home Front? with Thiemo Fetzer (University of Warwick), Oliver Vanden Eynde (PSE) and Austin Wright (Chicago)

Who Knows? An Experiment in Endogenous Network Formation, with Laura Derksen (Toronto)

Monitoring and Trust: the Effects of Body-worn Cameras on the Police Activity, with Daniel Barbosa (PUC-Rio), Caterina Soto (LSE) and Thiemo Fetzer (University of Warwick)

Rede de Vizinhos: An Experiment in Community Policing, with Caterina Soto (LSE) and Thiemo Fetzer (Warwick)

Alleviating Loneliness Among Migrant Garment Workers in India, with Heather Schofield, Achyuta Adhvaryu and Anant Nyshadham


Estimation and Selection of Spatial Weight Matrix in a Spatial Lag Model, with Clifford Lam (LSE), 2020

Journal of Business and Economic Statistics, Vol. 38, Issue 3


Spatial econometric models allow for interactions among variables through the specification of a spatial weight matrix. Practitioners often face the risk of misspecification of such a matrix. In many problems a number of potential specifications exist, such as geographic distances, or various economic quantities among variables. We propose estimating the best linear combination of these specifications, added with a potentially sparse adjustment matrix. The coefficients in the linear combination, together with the sparse adjustment matrix, are subjected to variable selection through the adaptive Least Absolute Shrinkage and Selection Operator (LASSO). As a special case, if no spatial weight matrices are specified, the sparse adjustment matrix becomes a sparse spatial weight matrix estimator of our model. Our method can therefore be seen as a unified framework for the estimation and selection of a spatial weight matrix. The rate of convergence of all proposed estimators are determined when the number of time series variables can grow faster than the number of time points for data, while Oracle properties for all penalized estimators are presented. Simulations and an application to stocks data confirms the good performance of our procedure.

A Test for Weak Stationary in the Spectral Domain, with Javier Hidalgo (LSE), 2019

Econometric Theory, Vol. 35, Issue 3


We examine tests for stability of the dynamics of a time series against alternatives that cover both local-stationarity and break points. One key feature of the tests is that the asymptotic distribution are functionals of the standard Brownian Bridge sheet in [0,1]^2 and do not depend on unknown parameters. The tests have nontrivial power against local alternatives converging to the null hypothesis at a T^{−1/2} rate, where T is the sample size. We examine an easy-to-implement bootstrap analogue and confirm the finite-sample performance in Monte-Carlo experiment. Finally, we implement the methodology to assess the stability of the inflation dynamics in the United States and on a set of neuroscience tremor data.

Detection and Estimation of Block Structure in Spatial Weight Matrix, with Clifford Lam (LSE), 2016

Econometric Reviews, Vol. 35, Issue 8-10


In many economic applications, it is often of interest to categorize, classify or label individuals by groups based on similarity of observed behavior. We propose a method that captures group affiliation or, equivalently, estimates the block structure of a neighboring matrix embedded in a Spatial Econometric model. The main results of the LASSO estimator shows that off-diagonal block elements are estimated as zeros with high probability, property defined as “zero-block consistency”. Furthermore, we present and prove zero-block consistency for the estimated spatial weight matrix even under a thin margin of interaction between groups. The tool developed in this paper can be used as a verification of block structure by applied researchers, or as an exploration tool for estimating unknown block structures. We analyzed the US Senate voting data and correctly identified blocks based on party affiliations. Simulations also show that the method performs well.

OTHER PAPERS and book chapters

Econometrics of Networks with Limited Access to Network Data: a literature survey, 2020

Forthcoming in the Handbook of Empirical Microeconomics

Testing for Equality of an Increasing Number of Spectral Density Functions, with Javier Hidalgo, 2013

Book chapter in "Topics in Nonparametric Statistics", edited by M.G. Atikas, S.N. Lahiri and D. Politis, Springer