CAMBRIDGE, MA -- In 2010, in the journal Nature, a pair of physicists at the Santa Fe Institute showed that when the population of a city doubles, economic productivity goes up by an average of 130 percent. Not only does total productivity increase with increased population, but so does per-capita productivity.
In the latest issue of Nature Communications, researchers from the MIT Media Laboratory's Human Dynamics Lab propose a new explanation for that "superlinear scaling": Increases in urban population density give residents greater opportunity for face-to-face interaction.
The new paper builds on previous work by the same group, which showed that increasing employees' opportunities for face-to-face interaction could boost corporations' productivity.
In those studies, the researchers outfitted employees of a bank, of an IT consulting firm, and of several other organizations with tiny transmitters, developed by the Human Dynamics Lab, that actively measured the time the wearers spent in each other's presence. Obviously, that approach wouldn't work in a study of the entire populations of hundreds of cities.
So Wei Pan, a PhD student and first author on the new paper, looked at a host of factors that could be used to predict what the researchers are calling social-tie density, or the average number of people that each resident of a city will interact with in person. Those factors include things like the number of call partners with whom a cellphone user will end up sharing a cell tower, instances of colocation with other users of location-tracking social-networking services like Foursquare, and the contagion rates of diseases passed only by intimate physical contact.
The availability of different types of data varied across the hundreds of cities in the United States and Europe that the researchers considered. But Pan and his colleagues concocted a single formula that assigned each city a social-tie-dens
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology