From Our Experts

Do Social Networks Increase or Decrease the COVID-19 Contagion Rate?

Matt Kahn, Bloomberg Distinguished Professor of Economics and Business and Director of the 21st Century Cities Initiative at Johns Hopkins University, and Dora L. Costa, the Kenneth T. Sokoloff Professor of Economic History at UCLA, discuss new social norms in the era of COVID-19.


Each nation will face less contagion risk if we as individuals engage in social distancing. But some people are choosing to continue to live their lives under business as usual. Behavioral economics assumes that many of us, like the college students who stormed the beaches of Florida for spring break, focus on the here and now and thus lack the willpower to self isolate at this critical juncture.

The desire to socialize pushes us to meet and interact face to face, but social capital, the bonds between us, can push us to self isolate. Social sanctions and the fear of ostracism can play a role in encouraging pro-social behavior at a time when only a few nations such as Italy (which is fining people for up to $3,300) and India (which is using corporal punishment in some cases) are using the formal power of the state to enforce social isolation. Social capital can decrease contagion risk because it helps solve the classic free rider problem of who is willing to engage in costly sacrifice for the common good. The free rider problem arises when socially beneficial actions impose costs on individuals and each person hopes that every other person will comply with the social norm. Our research documents that this problem is exacerbated when people live in more unequal communities as measured by income inequality and age and ethnic diversity.

Around the world, each nation is wrestling with how to utilize both the formal rule of law and social sanction to achieve the overall social goal of greater isolation compliance. In the biggest coronavirus success story thus far, Taiwan, mandatory quarantines are enforced by the neighborhood warden system, tracking of cell phones with follow-ups by police officers if phones are shut off, and periodic administrative checks on those in quarantine. In China, neighborhood committees enforced quarantines by taking temperatures and checking the travel permits of anyone entering a neighborhood. India has resorted to physical punishments such as canings for those found out and about. Italy introduced a formal deterrence system of fines and is using drones to look for quarantine violators after cell phone data showed informal deterrence failed. Israel’s Supreme Court approved tracking the cell phones of citizens with coronavirus after placing an injunction on the practice. South Korea has dramatically slowed its cases with testing, contact tracing, and individual quarantines but without lockdowns or authoritarian measures. Sweden is relying on individuals’ personal responsibility and sacrifice to self-quarantine. Sweden’s Prime Minister Stefan Löfven said; “The only way to manage this crisis is to face it as a society, with everyone taking responsibility for themselves, for each other and for our country.” The United States is relying on self-quarantines as well.

An alternative to force is to rely on nudges and social sanction to encourage compliance. Authority figures such as University Presidents are nudging people to isolate. The effectiveness of such appeals hinges on who is an “influential” in guiding the choices of others. For some it will be celebrities while for others it will be our leaders.

Without formal criminal or financial penalties for noncompliance, each nation is asking its citizens to sacrifice for the greater good. An interdisciplinary research agenda featuring contributions by political scientists, economists and sociologists has studied this issue by examining civic activities such as volunteering, filling out census forms or giving blood.

Our own research has documented that income inequality in the city where one lives is an important determinant of free riding and not being civically engaged. National rankings of social capital suggest that the U.S is ranked relatively low. Nations and communities featuring less social capital are more likely to face a greater free rider challenge such that fewer people comply with the social isolation goal and thus the disease contagion accelerates.

We have also studied distinctive measures of being civically engaged in high stakes settings in our work on the U.S Civil War. We have examined the records of more than 40,000 men who fought in the US Civil War. One of our indicators of civic engagement was not deserting from one’s unit. Desertion increased one’s own survival probability but it put the other men in the unit at risk. We document that soldiers are less likely to desert, and thus to sacrifice for the greater good, when the men in their unit were of the same ethnicity, occupation and age. The “band of brothers” mentality encouraged civic engagement. This camaraderie built up in these war communities helped men survive extreme conditions such as those in the notorious POW camp of Andersonville. Those imprisoned with their buddies could help each other and were more likely to survive.

Social isolation imposes higher costs on different people. Richer, more educated people have an easier time engaging in self isolation because their jobs can be completed at home and these people live in nicer, roomier spaces. Those who find Facebook and Skype to be a close substitute for face to face interaction, will face a lower cost of physical isolation. More social people will suffer more from social distancing but since these people have more friends who in turn are likely to have more friends, it is exactly for this group that we need to encourage them to sacrifice in the short run.

Nobody intends to accelerate contagion risk. Within tight social networks such as families, loved ones know who is the most likely to break the social rules. Norm enforces within such family networks have an incentive to anticipate these tendencies and to take actions to discourage such socially costly risk taking. Social pressure through the actions of families, neighbors and communities and celebrities influence our behavior and help to achieve aggregate risk reduction.