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Last updated: April 22, 2021


Modes of contagion, the spread of the virus and unidentified carriers

This paper studies contagion when information is scarce, spreaders are unknown, and people are contaminated through using the same device successively. Reducing the variance of the number of users via organizational measures always limits contagion, at no cost. This result partially extends to the oft-analysed simultaneous case. The gains from better organization can be substantial but they decrease with higher proportions of spreaders. This calls for early action at the beginning of an epidemic or after the end of a lockdown.


When to Release the Lockdown? A Wellbeing Framework for Analysing Costs and Benefits

It is politicians who have to decide when to release the lockdown, and in what way. In doing so, they have to balance many considerations (as with any decision). Often the different considerations appear incommensurable so that only the roughest of judgements can be made. For example, in the case of COVID-19, one has to compare the economic benefits of releasing the lockdown with the social and psychological benefits, and then compare the total of these with the increase in deaths that would result from an early exit. We here propose a way of doing this more systematically.


The Economic Cost of COVID Lockdowns: An Out-of-Equilibrium Analysis

We develop a model of production networks with out-of-equilibrium dynamics. The production network model allows us to study not only the direct cost of the lockdown but also indirect costs which emerge from the reductions in the availability of intermediate inputs. The model is calibrated to the world economy using input-output data on 56 industries in 44 countries including all major economies. Covid-19 lockdowns are implemented as partial reductions in the output of some sectors using data on sectoral decomposition of capacity reductions. We use computational experiments to replicate the temporal sequence of the lockdowns implement in different countries. China, Italy, Mexico, and France incur a high cost of the lockdowns as proportion of their GDP, while US, India, and Brazil are more moderately affected. World output falls by 7% at the early stage of the crisis when only China is under lockdown and by 23% at the peak of the crisis when many countries are under a lockdown. These direct impacts are amplified as the shock propagates through the world economy because of the buyer-seller relations. Supply-chain spillovers are capable of amplifying the direct impact by more than two folds.We also study the process of economic recovery following the end of the lockdowns. The world economy takes about one quarter to move towards the new equilibrium in the optimistic and unlikely scenario of the end of all lockdowns. Recovery time is likely to be significantly greater if partial lockdowns persist.


Excess mortality due to COVID-19 in French municipalities: poverty, housing conditions and labor market

This research project investigates the heterogeneity of the impact of COVID-19 on French municipalities’ mortality according to their economic affluence. We first document a substantial gap in excess mortality due to COVID-19 between poor and rich municipalities. Using rigorous statistical methods (triple difference), we are able to isolate the impact of COVID-19 from that of the lockdown. We then analyze to what extent the link between economic affluence and excess mortality can be explained by municipalities’ share of over-crowded houses, population density and socio-professional composition. Although these three dimensions do not cover all possible channels, a recent literature has shown that they are both a vector of transmission and/or exposure to the virus and a strong indicator of economic affluence.


Does Holding Elections during a Covid-19 Pandemic Put the Lives of Politicians at Risk?

Au début de 2020, la pandémie de Covid-19 a obligé la majeure partie de la planète à cesser toute activité non essentielle. La question de savoir s’il faut considérer les élections comme une activité essentielle dans ce contexte a fait l’objet d’intenses débats qui ont conduit à des décisions radicalement différentes à travers le monde. Les résultats empiriques permettant d’orienter les politiques publiques en la matière sont encore très rares. Ce projet de recherche vise à combler cette lacune en estimant l’impact de la tenue du premier tour des élections municipales françaises sur la mortalité des premiers intéressés, les conseillers municipaux et des candidats aux élections. Nous estimons l’impact des élections municipales françaises de la mi-mars 2020 sur la mortalité de 170 000 candidats masculins âgés de plus de 60 ans en utilisant l’appariement de plusieurs bases administratives. Nous trouvons que leur surmortalité en mars et avril a été similaire à celle de la population générale. Nous comparons ensuite les candidats des villes avec deux listes de candidats à celles des villes n’ayant qu’une seule liste, car les élections génèrent plus de contacts dans le premier groupe. Nous utilisons également un modèle de discontinuité de régression et nous étudions la mortalité en 2020 en fonction du résultat des candidats aux élections de 2014. Nous ne pouvons détecter aucun effet causal d’une participation active aux élections de 2020 sur la mortalité.


Compensating for Academic Loss: Online Learning and Student Performance during the COVID-19 Pandemic

The outbreak of the COVID-19 pandemic has led to widespread school shutdowns, with many continuing education via online-learning platforms. We here estimate the causal effects of online learning on student exam performance using administrative data from Chinese Middle Schools. Using the difference-in-differences approach, we find that receiving online education during the COVID-19 lockdown improved student academic results by 0.22 of a standard deviation, relative to pupils without learning support from their school. Not all online education was equal: students who were given recorded online lessons from external higher-quality teachers had higher exam scores than those whose lessons were recorded by teachers from their own school. The educational benefits of distance learning were the same for rural and urban students, but the exam performance of students who used a computer for online education was better than those who used a smartphone. Last, while except the very-best students benefited the most from online learning, it was low achievers who benefited from teacher quality.


Group Testing with Homophily to Curb Epidemics with Asymptomatic Carriers

The global fight against COVID-19 is plagued by asymptomatic transmission and false negatives. Group testing is increasingly recognized as necessary to fight this epidemic. I examine the gains from considering heterogenous interpersonal interactions, which induce potential contamination, when designing testing pools. Indeed, people interact in blocks, a feature known as homophily. Homophily can be identified ex ante at a scale commensurate with pool size, so that the risk of contamination is higher within a well-designed pool than with an outsider. This makes it possible to overcome the usual information-theoretic limits of group testing which rely on an implicit homogeneity assumption. More importantly, group testing with homophily detects asymptomatic carriers that would be missed even by exhaustive individual testing because of false negatives. To the best of my knowledge, this is the only test strategy that tackles this issue.Such a strategy should be implemented at least at a weekly frequency to fit the time profile of test positivity. At a time when 1.19 million tests are implemented weekly in France, such a strategy is now feasible.


How Laws Affect the Perception of Norms: Empirical Evidence from the Lockdown

Laws not only affect behavior due to changes in material payoffs (through fines and other kinds of sanctions), but they may also change behavior through a change in the perception individuals have of societal norms. This may happen either by shifting the norms directly (because the law is used to infer the approproate behavior in a given situation) or by providing information on pre-existing norms (through an informational channel). Using detailed daily survey data and exploiting the introduction of lockdown measures in the UK in the context of the COVID-19 health crisis, we provide causal evidence that the law drastically changed the perception of the norms regarding social distancing behaviors. We show this effect of laws on perceived norms is mostly driven by an informational channel as social norms themselves remain unchanged. We also show that people used to be overly pessimistic about the norm; the observed shift in the perceived norm results in a sharp reduction in the gap between individual normative views and social norms.


The Fall in Income Inequality during COVID-19 in Five European Countries

The authors use panel data from the COME-HERE survey to track income inequality during COVID-19 in France, Germany, Italy, Spain and Sweden. Relative inequality in equivalent household disposable income among individuals changed in a hump-shaped way over 2020. An initial rise from January to May was more than reversed by September. Absolute inequality also fell over this period. As such, policy responses may have been of more benefit for the poorer than the richer.