Sun, Jun 08, 2008 page9

• So predictable: cellphone users are easy to find

  • by John Schwartz / NY TIMES NEWS SERVICE
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  News flash: We’re boring. New research that makes creative use of sensitive location-tracking data from 100,000 cellphones in Europe suggests that most people can be found in one of just a few locations at any time, and that they do not generally go far from home.

  “Individuals display significant regularity, because they return to a few highly frequented locations, such as home or work,” the researchers found.

  That might seem like science and mountains of data being marshaled to prove the obvious. But the researchers say their work, which also shows that people exhibit similar patterns whether they travel long distances or short ones, could open new frontiers in fields like disease tracking and urban planning.

  “Slices of our behavior are preserved in these electronic data sets,” said Albert-Laszlo Barabasi, an author of the project and the director of the Center for Complex Network Research at Northeastern University in Boston. “This is creating huge opportunities for science.”

  The researchers said they used the potentially controversial data only after any information that could identify individuals had been scrambled. Even so, they wrote, people’s wanderings are so subject to routine that by using the patterns of movement that emerged from the research, “we can obtain the likelihood of finding a user in any location.”

  The researchers were able to obtain the data from a European provider of cellphone service that was obligated to collect the information. By agreement with the company, the researchers did not disclose the country where the provider operates.

  The researchers, including Barabasi’s Northeastern colleagues Marta Gonzalez and Cesar Hidalgo, tracked 100,000 cellphone users selected at random from a population of 6 million for six months.

  The location of the user was revealed whenever he made or received a call or text message; the telephone company would record the nearest cell tower and time.

  Because calls and messages tended to be sporadic, the researchers used a smaller data set that captured the location of 206 users every two hours. The results of the two data sets were similar, according to the report.

  Scientists have long wondered how to measure something as ephemeral as movement. If general rules and algorithms of people’s wanderings could be discerned, they could be used to create computer models for understanding emergency response, urban planning and the spread of disease, say the authors, whose work appears in the new edition of the journal Nature.

  Previous efforts to find data that can shed light on the movement of large groups of people have used complex formulas to predict behavior. But more recent efforts have involved the search for data in a seemingly unrelated area.

  One such paper, by Dirk Brockmann, a professor of physics at Northwestern University, tracks paper currency as a surrogate for the movement of people. Using data from the wheresgeorge.com Web site, where volunteers track the location and flow of more than 129 million bills of various denominations, Brockmann found similar routines of movement that also resemble those of animal foraging.

  The cellphone researchers pointed out that the new paper moved the field forward significantly because people hold on to their phones, and so the movement of individuals is more closely tracked than it can be with paper currency that is passed from person to person.

  As the researchers put it in the paper: “Dollar bills diffuse, but humans do not.”

  Both lines of research, however, suggested that people did not really move around much.

  Brockmann, who was a reviewer on the new paper, said he first approached it with some trepidation.

  “I said, ‘Oooh, I hope this does not completely falsify what we found,’” he said.

  Instead, he said, “I was very happy to see that it was consistent with what we found, even though the patterns of travel were obtained by very different sets of data.”

  The use of cellphones to track people, even anonymously, has implications for privacy that make this “a troubling study,” said Marc Rotenberg, a founder of the Electronic Privacy Information Center in Washington.

  The study, Rotenberg said, “raises questions about the protection of privacy in physical spaces, when devices make possible the capture of locational data.”

  There are serious ethical issues as well, said Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania.

  While researchers are generally free to observe people in public places without getting permission from them or review from institutional ethics boards, Caplan said, “your cellphone is not something I would consider a public entity.”
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