A team of theoretical physicists in German and the United States has used data from a website that tracks the movement of U.S. currency to come up with a mathematical model that could help predict how epidemic disease is spread.
Dirk Brockmann knew what he wanted: a source of raw data that would include airplane trips across oceans, as well as shorter trips by rail, road, bicycle and foot. It's just that he didn't have any idea where to find it.
"I knew what I would need for a model for the spread of disease," he said, adding that he needed to determine "the probability of a human traveling a certain distance -- how many journeys of 10 kilometers occur as opposed to journeys of 100 kilometers as opposed to journeys of, say, 1000 kilometers."
Dr. Brockmann, a theoretical physicist at the Max-Planck Institute for Dynamics and Self-Organization in Germany, was visiting a friend in the United States, and told him about his frustration. The friend -- a cabinetmaker, not a scientist -- immediately thought about Where's George.
WheresGeorge.com is an Internet-based game that tracks the movement of paper money around the United States. "And when I saw the website, I realized that this distribution of distances will exactly mimic the distribution of human traveling," recalled Dr. Brockmann.
Fifty million banknotes - many of them $1 bills featuring a portrait of President George Washington, our first president - have been registered in Where's George by their serial number. If a bill is logged a second time, you can see where it started, where it went, and how long it took to get there.
The creator of WheresGeorge.com says he was a bit reluctant to provide the data at first, as he had worked with other researchers in the past, but they never published their findings. At the end of the day, though, Hank Eskin says it was a good experience.
"The fact that somebody was able to take those data, convert it into something meaningful to support their theories and their research is wonderful," he said. "I think it's a wonderful thing. And if we can do it in the future for other projects, that would be good, too. The fact that it might be able to help humanity in some way, other than an interesting diversion on the Internet, is a wonderful thing, and I really applaud them for putting this together."
Back in Germany, Dr. Brockmann and his colleagues got records of almost a half-million currency movements from the website, which they then analyzed to produce a set of rules that could guide epidemiologists and public health officials as they prepare for the spread of a disease such as avian flu.
Once they had the data, it was a matter of finding the right mathematical equations to describe the movement of money ... or people, people who might carry disease. But Dirk Brockmann cautions that his work represents only one piece of the puzzle. "We presented a theory that accounts for the traveling only. And you have to understand [that] a model for the spread of disease consists of many ingredients -- travel only being one ingredient."
And he stressed that further testing and refinement of his model is needed.
"We will, of course, take our results and plug them into models that are constructed to account for the spread of, you know, modern diseases like SARS or influenza, or childhood diseases like measles. But we are not at that stage yet." said Dirk Brockmann, lead author of "The Scaling Laws of Human Travel," an article in the January 20 issue of Nature.