Paper trail of money shows likely path of flu

Internet site that tracks bills used to map possible outbreak


For public health authorities planning for the spread of a global flu pandemic, German scientists have this advice: follow the money.

The researchers have discovered that the movements of paper currency, as tracked by a popular Internet game site called "Where's George?" can serve as a useful proxy for human travel. And that may give health officials a more realistic model for predicting how deadly pandemics would spread.

No one is more surprised and delighted than Hank Eskin, 41, the Boston computer consultant whose idle curiosity launched "Where's George?" in 1999.

"I think it's fantastic," he said. "For the last many years there have been certain naysayers and critics who criticized [the game] as a useless waste of time."

Well, he said, "it may be useless for a lot of people. But on the other hand, it may be useful to predict an epidemic. And if it helps one person, that's great."

Eskin and a handful of other "Georgers," as players call themselves, planned to meet at the Baltimore Convention Center this morning to listen as Dirk Brockmann and Theo Geisel describe their research for physicists at a meeting of the American Physical Society.

The talk, which is open free to the public, begins at about 11:50 a.m. in Room 325.

Brockmann and Geisel are with the Max Planck Institute for Dynamics and Self-Organization in Gottingen, Germany. Their third research partner, Lars Hufnagel, is a theoretical physicist at the University of California, Santa Barbara.

Their paper was first published in January in the journal Nature.

"Where's George?" began on a whim when it occurred to Eskin that a bill could be tracked online by its unique serial number. "It was a quirky idea," he said. But it was just what he had been looking for.

"My objective was to learn the [Web] technology, so that when I had the `big idea,' I'd be ready to go," he said. "Little did I know this actually would become the big idea."

It's a pretty simple one. Players register themselves and their bills' serial numbers. Then they stamp the bills with the "Where's George?" Web address, and spend the money.

As the bills move through the economy, some people who get them in change notice the "Where's George?" markings, visit the Web site and enter the serial number. That, in turn, brings up the history of the bill's travels, and everyone who has entered the number gets an update on where it has been and who has handled it.

Georgers compete with each other, gab and share stories on an online forum. They even gather for local and national George fests.

Thousands of bills

Charles Moment, a statistical analyst for the Social Security Administration in Baltimore, began marking his cash in 2001 after he found a "Where's George?" bill in his change. "I decided this looks like a fun thing to do," he said.

He's since launched about 10,000 "Where's George?" bills. And he checks on them every day. About 12 percent have been found and re-entered over the years, scoring "hits" on the Web site.

"Most of them stay in the Northeast," he said. But "once in a while someone will catch a plane. I've had bills show up in Poland and Turkey."

In all, 3.4 million people have registered since 1999, entered 79 million bills and received 8.8 million hits. More than 6,700 people are active on the site in a typical day.

"Some people do it for the pure statistics of it," Eskin said. "Some people like mapping where their hits go. There's the social aspect of communicating with the people who find their bills."

Brockmann and his colleagues stumbled on the site, and quickly realized its potential.

"For some time we have been asking ourselves how to quantify human travel," Brockmann said, "because if you want to develop realistic models for the spread of infectious disease -- pandemics, that sort of thing -- you need to know how humans travel."

It was always presumed that modern travel was too complex to be easily reduced to a mathematical formula that could be plugged into a computer model for the spread of disease.

In the Middle Ages, the plague spread at the walking speed of a human or horse. It took three years for the virus to cross the European continent. And it moved predictably in what physicists call a "wave front" -- diffusing like the ripples on a pond.

But people today move across short and long distances, using cars, planes, trains, buses and other transport modes -- at speeds ranging from a walk to an airliner's 500-plus miles per hour.

When they discovered Georgers, Brockmann and his colleagues saw that the cash could be a statistical proxy for people, "because money is transported by people," Brockmann said.

Eskin initially rebuffed the scientists' request for data. He had helped other researchers before, and nothing ever came of it. "I wasn't crazy about doing it again," he said.

So Brockmann and his team wrote a program that automatically extracted the data they needed from the Web site, and began working with it.

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