David Warsh: The mysterious machinery of epidemic models

“The Plague of Athens ‘‘ by Michiel Sweerts (painted in 1652-54), illustrating the devastating epidemic that struck Athens in 430 B.C., as described by the historian Thucydides.

SOMERVILLE, Mass.

It is not difficult to identify a 9/11 moment in the 2020 COVID-19 pandemic, an event after which everything changed. Until mid-March, politicians in Britain and the United States were cautiously optimistic. Prime Minister Boris Johnson advised, “We should all basically just go about our normal daily lives.”  President Trump, in an Oval Office address on March 11, said that for the vast majority of Americans, the risk is very, very low.”

Five days later, on March 16, the British government took the first of a series of measures leading to a lockdown on March 23.  On March 17, President Trump read a statement to a press briefing:

My administration is recommending that all Americans, including the young and healthy, work to engage in schooling from home when possible. Avoid gathering in groups of more than 10 people. Avoid discretionary travel. And avoid eating and drinking at bars, restaurants and public food courts. If everyone makes this change or these critical changes and sacrifices now, we will rally together as one nation and we will defeat the virus. And we’re going to have a big celebration all together. With several weeks of focused action, we can turn the corner and turn it quickly.

What happened? Imperial College, London, released a model-based study on March 16 that made headlines around the world, predicting as many as 2.2 million deaths might occur in the U.S., and 510,000 in the U.K. as a result of the pandemic.  To this point, 265,000 US deaths have been reported, and another 58,030 in Britain.

Since March, economists have gone to work seeking to better understand the machinery of epidemiological models and the theories on which they are based.  In “An Economist’s Guide to Epidemiology Models of Infectious Disease,” in the Journal of Economic Perspectives, Fall  2020, Christopher Avery, William Bossert, Adam Clark, Glenn Ellison and Sarah Fisher Ellison lay out the facts above, along with some of their findings.

Epidemiology has become more empirical over time, they say, and epidemiologists are learning to add parameters to their models. But they make less of a distinction between theory and empirical approaches than do economists. Meanwhile, “a model which posits a symmetric, bell-shaped evolution of cases over time cannot accommodate repeated changes in the rate of spread due to changing regulations, changing public perception, and ‘quarantine fatigue.’”

Not surprisingly, economists have begun looking for means of suppressing the virus by changing behaviors in manners as cost-effective as possible.  Representative is James Stock, of Harvard University, who argued in September that lockdowns are too are too blunt a method to rely on in most cases. In “Policies for a Second Wave,”  for a special summer edition of Brookings Papers on Economic Activity, Stock and David Baqaee,  Emmanuel Farhi and Michael Mina proposed framing the wearing of masks as a patriotic duty, pursuing cheap and rapid testing, stressing contact tracing and quarantine, and implementing waste-water testing as a means of surveillance once the virus is suppressed.

Epidemiology is not the only discipline to come under economists’ lens. Bruce Sacerdote, Ranjan Schgal and Molly Cook ask Why Is All Covid-19 News Bad News? in a National Bureau of Economic Research working paper out this month. They fault mainstream media for underplaying news of vaccine trials and school re-openings. Ninety-one percent of articles  by U.S. major media outlets have been negative in tone since the first of the year compared with 54 percent abroad and 65 percent in scientific journals. Stories discussing Donald Trump and hydroxychloroquine were more numerous than all stories combined about companies and individuals working on a vaccine, they complained.

Of course those stories about hydroxychloroquine may have been more about the nature of the president’s leadership than about COVID-19.  Even so, there is indeed evidence of hierarchy and momentum in the reporting: what Wall Street Journal columnist Holman Jenkins, Jr. goes on about.  It’s going to be a long time before the strange coincidence of Donald Trump and the virus is untangled.  Integrated assessment of the pandemic has far to go.

David Warsh, a veteran columnist and an economic historian, is proprietor of economicprincipals.com, where this piece first ran.