As my family has dealt with a round of (thankfully mild) covid-19 infections over the past couple weeks, I have been motivated to look at some academic research about covid as it relates to urban design and housing policy.

In this post I’ll be looking at Hamidi et al. (2020) “Does Density Aggravate the COVID-19 Pandemic? Early Findings and Lessons for Planners,” which was published in the Journal of the American Planning Association (side note: this article is available for free).

The authors use a statistical method called a structural equation model to test influences on their dependent variables, which are the rate of COVID-19 infections and deaths per 10,000 population, based on data from 913 metropolitan counties across the United States. The big conclusion is that larger metropolitan areas do have higher COVID infection and death rates, but once you control for the population of the metro area, there is no statistically significant relationship between the density of the county and the COVID infection rate and denser counties have lower COVID death rates.

The authors explain this by making a distinction between connectivity and density. Large metro areas, like the Los Angeles-LongBeach-Anaheim Metropolitan Statistical Area, which we live in, tend to be better connected to the wider world and have more business travel. Thanks to our multiple airports, our region has direct links not only across the country, but across continents. That makes it easier for pandemics to arrive here in the first place.

However, denser counties also tend to have higher-quality health care systems, and this is a mitigating factor for COVID deaths: higher numbers of ICU beds per capita are associated with lower COVID death rates. This confirms intuition, but it’s nice to have it meticulously demonstrated statistically.

This study was conducted early in the pandemic, with data from May 2020, and the authors are the first to point out that their conclusions may need to be reassessed once more time passes and scholars have had the opportunity to conduct longitudinal studies, instead of just looking at a cross section of data based on a single point in time.

The study highlights some other interesting relationships. For example, there’s a strong positive correlation (meaning an increase in the independent variable is associated with an increase in the dependent variable) between African American population and COVID infections. This is due to the manifestations of structural racism, including higher prevalence of pre-existing health conditions in this population and lower access to safer workplace policies, like the ability to socially distance at work, for example, by working remotely.

Looking back historically, the authors note that the 1918 Influenza Pandemic was most severe in rural and other low density areas, when you look at case rates (cases per capita) instead of just the absolute number of cases. Of course you would expect more cases where there are more people, but what matters is the odds of a given person getting sick in a given place, which is about the case rate.

So should planners throw out the concept of dense cities because of COVID? Absolutely not. On the contrary:

“Our findings suggest that planners should continue to practice and advocate for compact places rather than sprawling ones due to several environmental, transportation, health, and economic benefits of compact development confirmed by dozens of empirical studies.”

I love this quote. The benefits of compact development have been confirmed by dozens of empirical studies. Take that line to your next city council meeting.

Instead, what planners and advocates can do to mitigate pandemics is to advocate for proven public-health measures, which in the context of 2020, included a lot of social distancing, but which could also include interventions like vaccinations, testing, masking, and ensuring broader access to basics like paid sick days, health care and housing.

COVID-19 has left a lasting mark on our society and a range of public policy debates. It’s critically important that housing policies be grounded in evidence. We need to dramatically expand the supply of infill housing, better fund affordable housing and protect tenants, so that people can afford to cover their basic needs and we can reap the benefits to the environment, transportation, public health and the economy.