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    • COVID-19 Business Impact Center
      COVID-19 Business Impact Center
      Social Interactions in Pandemics: Fear, Altruism, and Reciprocity
      01 Jul 2020Working Paper Summaries

      Social Interactions in Pandemics: Fear, Altruism, and Reciprocity

      by Laura Alfaro, Ester Faia, Nora Lamersdorf, and Farzad Saidi
      An analysis of 89 cities worldwide shows that mobility responds to infection risk, altruism, and reciprocity. Correcting the SIR model to account for this behavior shows that a balanced approach involving stringency measures, in respect of human dignity, and responsible social preferences mitigates the pandemic health and economic costs.
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      Author Abstract

      In SIR (“S,” the number of susceptible, “I,” the number of infectious, and “R,” the number of recovered, deceased, or immune individuals) models, homogeneous or with a network structure, infection rates are assumed to be exogenous. However, individuals adjust their behavior. Using daily data for 89 cities worldwide, we document that mobility falls in response to fear, as approximated by Google search terms. Combining these data with experimentally validated measures of social preferences at the regional level, we find that stringency measures matter less if individuals are more patient, exhibit altruistic preference traits, and exhibit less negative reciprocity community traits. We modify the homogeneous SIR and the SIR-network model to include agents' optimizing decisions on social interactions. Susceptible individuals internalize infection risk based on their patience, infected ones do so based on their altruism, and reciprocity matters for internalizing risk in SIR networks. A planner further restricts interactions due to a static and a dynamic inefficiency in the homogeneous SIR model, and due to an additional reciprocity inefficiency in the SIR-network model. We show that partial or targeted lockdown policies are efficient only when it is possible to identify infected individuals.

      Paper Information

      • Full Working Paper Text
      • Working Paper Publication Date: May 2020
      • HBS Working Paper Number: NBER Working Paper Series, No. 27134
      • Faculty Unit(s): General Management
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      Laura Alfaro
      Laura Alfaro
      Warren Alpert Professor of Business Administration
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