The limits of smartphone data on display as country seeks to reopen
Federal and state officials are using smartphone location data to inform what amounts to a high-stakes public health experiment in reopening the economy while a lethal pandemic remains rampant.
But the value of that data is unproven in predicting when and how to relax restrictions, and epidemiologists are uncertain that the data will be as useful in forecasting the likely result of allowing nail salons, restaurants and movie theaters to reopen as it was in tracking the public’s adherence to stay-at-home orders issued in the early weeks of the pandemic.
More than four months after a novel coronavirus emerged in China, this is just one of many key questions about the pandemic that remain subject to scientific inquiry and debate: How much do masks slow transmission? Does warmer weather impede the coronavirus? How vulnerable are children? What is the infection risk on increasingly crowded beaches and parks? Are the people who have survived covid-19, the disease caused by the coronavirus now immune?
Where people travel and how long they stay away from home can be measured with smartphone location data. But the increasingly popular movement maps derived from this data don’t reveal how well people maintained social distancing once they reached their destinations – something that is key to understanding the transmission of the coronavirus,epidemiologists say.
“In general, more movement does increase the risk of transmission, but you also have to take that with a grain of salt,” said Saskia Popescu, a George Mason University epidemiologist. “It’s not a crystal ball. It’s a forecasting process.”
The influential pandemic modelers at the University of Washington recently plugged location data – gleaned from millions of smartphones – into their equations to reflect the growing restlessness of Americans as a sweeping national shutdown approached the two-month mark.
The results were alarming: Projected mortality from covid-19 nearly doubled. Long-term hospital demand soared. A predicted period of summertime calm abruptly vanished, replaced by a grim stretch in which hundreds of people were expected to die each day. Put simply, the modelers had come to believe that as Americans resumed traveling more widely, a new wave of infection and death surely would follow.
But that conclusion, while widely shared by public health authorities eyeing the same smartphone data, is at least one step beyond what the science can reliably show at this point, epidemiologists say. Although more traveling almost certainly means more transmission, the amount depends on the subtleties of human interaction – How close did people stand? Did they sneeze? Were there physical barriers such as a closed car window? – that smartphone location data does not reveal.
This distinction may seem academic, but it bears on the urgent and unresolved national question of whether Americans can resume some semblance of their previous lives while still limiting the spread of the deadly virus.
These unknowns – combined with the ongoing national failure to deploy adequate testing and contact tracing – have left policymakers grappling in the dark, fearing that the wrong advice could unleash a new wave of infection or, conversely, worsen economic devastation that has drawn comparisons to the Great Depression.
“Anyone who speaks with a lot of confidence about how this plays out hasn’t thought very deeply about it,” said Eli Fenichel, a Yale University professor of natural resource economics who has studied the relationship between location data and the spread of disease.
Among the most closely scrutinized scientific products during the pandemic have been models, such as the University of Washington’s, that attempt to show the future trajectory of covid-19 infection and death. Though initially built to anticipate demand for resources, especially at hospitals, pandemic models have been embraced more broadly by policymakers forced to make decisions with little meaningful precedent for guidance.
Marketers of smartphone location data – derived mainly from mobile apps and sold primarily to advertisers or analysts looking for insights into consumer behavior – began building free dashboards of aggregated, anonymized data in March. Facebook and Google also released their own maps of community movement, based on data from smartphones running their software.
Never before had so much information on the collective locations of Americans been so readily available and easily visualized.