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The Elegant Mathematics of Social Distancing


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The Elegant Mathematics of Social Distancing

Schools and sports leagues are shutting down. But experts say it's still safe for most people to shop for groceries and meet in small groups.
Photograph: Laurence Griffiths/Getty Images

My cousin had to cancel his bar mitzvah, which was planned for Saturday in Washington, DC. Some 100 people were scheduled to be there, but like many houses of worship this week, the synagogue suspended its services to help prevent the spread of the coronavirus. For my cousin, it means postponing the payoff from years of study, and a celebration with friends and family.


Many other Americans are in similar situations during the outbreak of Covid-19, which has sickened more than 1,700 Americans and killed more than 40, according to an online tally being kept by Johns Hopkins University. Schools, religious institutions, and sports and concert venues have closed. Those who can work from home have been urged to do so. The White House reportedly overruled a proposal from the Centers for Disease Control that would have urged anyone over 60 to avoid airplane travel.


In states and cities around the country, gatherings of 500, 250, or sometimes even 75 people have been forbidden. The term “social distancing”—that is, public health measures to reduce the spread of a highly contagious disease—has become one of those particular pieces of field-specific esoterica that’s vaulted into the American vernacular, like “obstruction of justice” or “security theater.”


But people have lives: weddings to attend, kids’ birthday parties to endure, commutes to make, bonkers grocery store lines to stand in. What is safe right now? What isn’t?


The answer isn’t clear, given what researchers know—and don’t know—about the disease. And even experts aren’t united in their responses.


“This is not black and white,” says Ben Lopman, an infectious disease epidemiologist at Emory University’s Rollins School of Public Health. “We're trying right now to increase social distancing to slow down transmission of this infection. But that doesn't mean no human contact for the foreseeable future. It means us all taking sensible steps and doing our part to reduce the amount of interactions we have.”


Go to the grocery store, Lopman says, but maybe take one big trip rather than three smaller ones. Other experts suggest staying about six feet away from other people, if you can. If the person in front of you keeps coughing, maybe choose another line.


To some degree, the sorts of things you should be doing right now depend on who you are. Are you someone at higher risk, like over age 60, or someone with a chronic medical condition like heart disease, diabetes or lung disease? Do you often come into contact with someone with those conditions? Are you exhibiting any Covid-19 symptoms, like fever, cough, or shortness of breath? Have you been in contact with anyone who has? Check any of those boxes, and you might want to be more careful about where you go and who you interact with.


But “if you feel pretty sure that those answers to those questions are ‘no,’ you can get together [with others with similar answers] and play board games,” says Katie Colborn, a biostatistician and assistant professor at the University of Colorado at Denver.


“We all have to make contacts with people while we live our lives, what we should aim to do is to limit them, and certainly not to add more,” says William Hanage, an associate professor of epidemiology at Harvard’s Chan School of Public Health. “This may seem silly if your community is not yet reporting infections, but it is best to get used to thinking this way.”


From a mathematical perspective, determining how big a crowd is safe depends on a couple of key questions: How many people in a given area are infected with the disease? And how big is the event? If you know those things, you can estimate the probability of someone getting infected at the event. An elegant “Covid-19 Event Risk Assessment Planner” by the Georgia Tech quantitative biologist Joshua Weitz makes the following calculation: If, say, 20,000 cases of infection are actively circulating the US (far more than are known so far), and you host a dinner party for 10 folks, there’s a 0.061 percent chance that an attendee will be infected. But if you attend a 10,000-person hockey match, there’s a 45 percent chance. Hence the suspension of the NHL season, along with the NBA, March Madness, and Major League Baseball.


Unlike in a flu epidemic, there’s no underlying immunity in the population, meaning if you come in contact with the fluids of an infected person, you’re likely to get sick. In light of these sorts of calculations, and the fact that the virus seems to be spreading throughout a number of American communities, “it makes sense to do things like cancel mass gatherings and schools,” says Lopman.


Public health experts like social distancing for three reasons. For one, it likely “flattens the curve,” or decreases the number of infections at one time, or even overall. That helps prevent overloading the health care system, with its limited number of doctors, nurses, beds, and equipment like ventilators. Also, it buys time for a vaccine to be developed, says Catherine Troisi, an infectious disease epidemiologist at the University of Texas Health Science Center at Houston and the former assistant director of the Houston Health Department. (Officials hope to have a coronavirus vaccine available in 12 to 20 months.)


Data from China and South Korea have given researchers a general sense of the severity of the disease: It seems, right now, that 3.4 percent of known Covid-19 infections result in death. But that number isn’t for sure. And researchers still don’t know how contagious the disease is—that is, how many other people a single infected person may infect. And they don’t know how many cases there are in the US, because testing in most of the country has been slow to ramp up. All those unknown variables mean that everything at this point is a guesstimate.


When public officials set cut offs for mass gatherings—500, or 250, or 150 people—they’re deciding how risk averse they are, and balancing economic and social concerns. “There’s a lot of other consequences of canceling gatherings, and you have to weigh those. Workers need to work to pay their rent and not go homeless, because that might create a worse public health situation,” says Troisi, the epidemiologist and former public health official.


Troisi is making her own personal tradeoffs. “We are going, hell or high water, to St. Louis next week because we haven't seen those grandbabies in a long time,” she says. She and her husband plan to take an airplane from their home in Houston. She notes that, yes, they are both over 60, and therefore at higher risk. No, she will not travel if she comes down with a fever.


Stay tuned for the invite to my cousin’s rescheduled bar mitzvah. Like many plans right now, his are up in the air.



Source: The Elegant Mathematics of Social Distancing (Wired)

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Millenials have no problems with social distance. They sit 4 feet apart but would rather text than talk to each other. Back when i was growing up Bulling was in person, now they do it online. I am just amazed how they can walk, text and not hit a sign on the sidewalk. 


Just kidding Millenials. Don't worry the generation after you is even worse.



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