Urban density and COVID-19: understanding the US experience

Abstract

This paper revisits the debate around the link between population density and the severity of COVID-19 spread in the USA. We do so by conducting an empirical analysis based on graphical evidence, regression analysis and instrumental variable strategies borrowed from the agglomeration literature. Studying the period between the start of the epidemic and the beginning of the vaccination campaign at the end of 2020, we find that the cross-sectional relationship between density and COVID-19 deaths changed as the year evolved. Initially, denser counties experienced more COVID-19 deaths. Yet, by December, the relationship between COVID deaths and urban density was completely flat. This is consistent with evidence indicating density affected the timing of the outbreak—with denser locations more likely to have an early outbreak—yet had no influence on time-adjusted COVID-19 cases and deaths. Using data from Google, Facebook, the US Census and other sources, we investigate potential mechanisms behind these findings.

Critical Commentary: The city and the virus

“… Carozzi and co-authors (2020) show that their results are partly explained by big-city dwellers who can adapt by socially distancing, most obviously by working at home. Mongey et al (2020) show that US metro areas with larger shares of jobs that can be done remotely experienced larger drops in mobility during the first wave.…”

“…One set of theories highlights how urban density and interaction diffuse disease, especially via superspreading events. Just as agglomeration economies scale with city size, so may bigger cities’ vulnerability to pandemics ( Batty, 2020 ; Florida and Mellander, 2020 ; Glaeser, 2020 ; Stier et al, 2020 ), at least in the early stages ( Adler et al, 2020 ; Carozzi et al, 2020 ). Big cities and pandemics have a long history ( Florida et al, 2021 ; Glaeser, 2020 ); but more developed countries have largely forgotten about these urban public health challenges ( Batty, 2020 ).…”

Cities in a pandemic: Evidence from China

“…15 Interestingly, the FOD transformation is related to the within transformation and is a special case of the general , and the general orthonormal transformed variables are obtained 12 The FOD transformation is often referred to as Helmert's transformation in the literature. See for details Arellano andBover (1995, p. 41), andCameron andTrivedi (2005, p. 759). 13 The first difference (FD) transformation shares the same property, but the within transformation does not.…”

“…Almagro and Orane-Hutchinson (2020) also find a positive relationship between population density and confirmed cases across New York City zip code areas and Desmet and Wacziarg (2020) show similar patterns across US counties. Carozzi et al (2020) use instrumental variables based on historical information to address the potential endogeneity of urban density and obtain similar patterns. 7 Overall, the evidence seems to suggest that high population density in urban areas impose inherent public health risks during a pandemic.…”

Exploratory Study of Determinants of the Spread of COVID-19 before Shelter-in-Place Orders

“…Hamidi et al found no significant relationship between COVID-19 infection rate and activity density ( 14 ). Carozzi et al also found no association between population density and COVID-19 cases in the U.S. ( 17 ). In contrast, Wheaton and Kinsella Thompson found a significant relationship between population density and the number of cumulative cases in the U.S. at the county level ( 18 ).…”