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Tracking the movements of 100 000 people over six months through cell phone use, the researchers discovered that highly variable individual travel patterns collapsed into a single mathematical formula of probability.
"Despite the diversity of their travel histories, humans follow simple reproducible patterns," said co-author Cesar Hidalgo of Northeastern University in Boston.
Truly creatures of habit, most people migrate consistently to the same handful of spots, with occasional "long hops" to more distant locations, said the study, published in the British journal Nature.
"Less than three percent of people move regularly over more than 100 miles (170 kilometres)," Hidalgo told AFP.
Human movement hard to track
Predicting the movement of people during an epidemic, after an earthquake or in a traffic jam following a big football match has always been something of a guessing game for scientists, despite the huge stakes involved.
Companies whose profitability depends on knowing where individuals go and when - billboard advertisers, transporters, housing developers - have also been unable to crack the inner codes of human movement.
Part of the problem has been the lack of reliable data. One study of human mobility traced the distribution of half-a-million bank notes through a population, using the bills as a proxy for movement.
But notes change hands from owner to owner, breaking the thread of an individual's migration.
How the research was done
A team lead by Albert-Laszlo Barabasi, a professor at North-eastern, figured out a clever way around this shortcoming. Randomly selecting 100 000 anonymous cell phone users from a pool of six million, the researchers tracked individual movement through calls made and received by recording the location of the nearest relay tower.
Despite a total of more than 16 million "hops" from one spot to the next, "the resulting statistics show a strikingly small scatter" and thus add weight to the mathematical laws they disclose, commented Nature in an editorial.
Even without knowing why people go where they go, the patterns uncovered could, for example, provide crucial data on how to curb the spread of a communicable disease.
Up to now, epidemic models lacked detailed data on human mobility and had to rely on assumptions about random motion or computer simulations, said Hidalgo.
"Our results show that there are indeed some simple rules that can be used to describe human mobility," he said, adding that the same type of problems apply to urban planning and traffic forecasting.
"Epidemiologists will no longer be forced to work with highly oversimplified models of infection rates and disease spread," commented Nature. – (Sapa)
June 2008
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