JUST AS COVIDThe -19 turned everyday life upside down, so it changed civic rituals. Historically, the majority of Americans have voted in person. But in 2020, many states made postal voting easier, to reduce the risk of the virus spreading. The share of votes cast by correspondence climbed to 46% from 21% in 2016.
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Nevertheless, some 85 million people still voted in person. Did this contribute to the increase in the number of covid-19 cases in the United States at the end of last year?
Data from early 2020 is inconclusive. In Wisconsin, 450,000 people voted in person in a primary election in April. Two studies later in the month found no unusual increase in covid-19 cases; a third, released in May, has found a great effect.
The November general election offered richer data. So far, 20 states have released the number of ballots in each county cast by each method. Overall, places where a high proportion of votes were cast in person on election day – distinct from postal votes and votes submitted in person before elections – also had high covid-19 rates. However, this pattern can occur for reasons other than polling queues.
To help rule out alternative explanations, we investigated changes in the incidence of covid-19 within states over time. First, we compared each county’s case rate with its state average. There are many factors that can make illness more or less common in a state, such as super-spray events or mask warrants. Examining the gap between a county’s numbers and those for its state eliminates the impact of such events.
Next, we followed the evolution of these disparities between the pre- and post-election periods, a method known as “difference in differences”. Suppose that people who would not have been infected otherwise catch the virus in the polling stations. If so, the cases of covid-19 in the counties with the most in-person votes in a state should have either increased unusually quickly or decreased unusually slowly after the election.
The data shows exactly such a pattern. From mid-October to early November, cases of covid-19 in counties with the highest in-person turnout in their states fluctuated in the same way as those in areas with the highest in-person voting rates. lower. But a week after the election, positive tests became more common in places with the highest in-person turnout on election day. The gap was largest after 20-25 days, shortly after official data would include people infected by people who caught the virus by voting.
This discrepancy does not prove that the voting sites were at fault. Places with a lot of in-person votes on election day also tended to share other attributes, such as relatively low income and education levels and having voted in 2016 for Donald Trump, skeptical of masks and social distancing. Such characteristics could also have caused the striking “difference in differences” in the incidence of covid-19.
To isolate the impact of in-person voting, we built a model to predict each county’s post-election changes in covid-19 rates, relative to state averages. We tested 22 variables, such as population density and pre-election growth rate of covid-19 cases.
Many of these factors have had an impact on the spread of the virus. Yet after taking them all into account, voting in person still had a statistically significant effect. Holding the other variables constant, the difference in in-person voting on election day between the state with the highest rate in our data (Alabama, at 41% of the population) and the lowest (Arizona, at 6 %) was associated with 173 cases per 100,000 population. This implies that if no one had voted in person on election day, 220,000 fewer people would have been diagnosed with covid-19.■
Sources: State election data; Town hall; Administration of health resources and services; United States Census Bureau; US Election Performance Survey; New York Times
This article appeared in the Graphic Detail section of the print edition under the title “Stamped”