Web game provides breakthrough in predicting spread of epidemics

Using a popular internet game that traces the travels of dollar bills, scientists have unveiled statistical laws of human travel in the United States, and developed a mathematical description that can be used to model the spread of infectious disease in this country. This model is considered a breakthrough in the field.

“We were confident that we could learn a lot from the data collected at the www.wheresgeorge.com bill-tracking website, but the results turned out far beyond our expectations,” said Lars Hufnagel, a post-doctoral fellow at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara and co-author of an article describing the research in the January 26 issue of the journal Nature.

The worldwide spread of disease –– particularly pandemics with disastrous consequences for human health and economics –– has become a serious threat in the globalized world of intense international trade and travel. The threat of bird flu, the possible emergence of a new human “supervirus,” and the potential of a worldwide flu pandemic, make predicting the spread of these diseases more urgent than ever.

Historical pandemics, like the 14th-century plague, moved slowly in waves across geographical areas, because in the Middle Ages people could typically only travel a few kilometers a day. The speed with which epidemics could spread was thus kept in check. It took the plague three years to move up the European continent, south to north, with an average rate of spread of about two kilometers a day.

“But today people move great distances in short time periods, as well as short distances, and they use variable means of transportation,” said Hufnagel. “Thus we can expect that future pandemics will spread according to other rules, and more quickly. The rapid worldwide spread of SARS (severe acute respiratory syndrome) has already demonstrated this.”

Searching for a way to model the modern spread of disease became the focus of discussions among the co-authors: Theo Geisel, director of the Max Planck Institute for Dynamics and Self Organization and professor at the University of Goettingen; Dirk Brockmann, a postdoctoral fellow at the Max Plank Institute for Dynamics and Self Organization; and Hufnagel. Following a conference in Montreal, Brockmann met with a friend in Vermont, a cabinetmaker, who showed him the internet game for tracking the movement of dollar bills, located at www.wheresgeorge.com. Participants can register a dollar bill, of any denomination, and monitor its geographic circulation.

The physicists were intrigued: Like viruses, money is transported by people from place to place. They found that the human movements follow what are known as universal scaling laws (from local to regional to long-distance scales). Using the game data, they developed a powerful mathematical theory that describes the observed movements of travelers amazingly well over distances from just a few kilometers to a few thousand. The study represents a major breakthrough for the mathematical modeling of the spread of epidemics.

“Since we can’t track people with tracking devices, like we do animals, we needed to get data that provided us with millions of movements of individuals,” explained Hufnagel. Scientists are already familiar with similar scaling laws from physical and biological systems. “What is amazing about these particular scaling laws is the fact that they are determined by two universal parameters only. This result surprised us all.”

Added Brockmann: “We recognized that the enormous amount of data, as well as the geographical and temporal resolution of bill-tracking, allowed us to draw conclusions about the statistical characteristics of human travel, independent of which means of transportation people use.”

Geisel said, “We are optimistic that this study will drastically improve predictions about the geographical spread of epidemics.”

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30 thoughts on “Web game provides breakthrough in predicting spread of epidemics”

  1. we’ll see more of this kind of observation of nature in the future, where we take tons of data, like the dollar bill circulation data; run it through fast equipment like these computers here brakes parts

  2. but thats just the point, you dont have to go there, the virus is on your money (and so is cocaine residue and sweat from the local strip club)handle some ones and then touch your eye… i dare you! the problem with wheresgeorge is that if a bill changes hands 100 times maybe one person will actually reenter the bill… if everybody did it you would see some cool stuff. its not about somebody in nj flying to la, its about somebody in nj buying bread at 7-11, having it go into some one elses change to wind up in a gas station down the block before someone else uses it to pay a toll on the turnpike and 1285 transactions later its in a vending machine in vegas.if everybody who touched it entered it you would get a scary model

  3. US currency does travel overseas frequently, especially larger denominations as some countries require nothing less for exchange purposes. At least one of the most documented dollar bills on that website, A1473—0F, traveled from Illinois to Australia, then Philippines, then Korea, then back to the US, then New Zealand, then China, then Singapore, most of that between Oct 2003 and Oct 2005.
    Since the bill will pass through many hands that won’t actually document its whereabouts, we have no idea of knowing if other bills that were undocumented had actually left the US, and then returned.

  4. Making the assumption that flu pandemics will move in the same way is money is fine. However, says nothing about national borders. How would a pandemic leap from the USA to Japan, for example, or China, where dollar bills are a real rarity.

  5. Lots of potential for skewed data here.

    Just because a dollar bill you spent in one city turns up in another does not mean *you* went there, as stores and banks ship money around in large quantities. Also, the “Where’s George” game is voluntary and certainly not played by everyone who handles a particular bill, which might well travel unreported through a dozen states before reaching someone who chooses to report it.

    An interesting little diversion, but a long way from definitive.

  6. Their research isn’t about the Middle Ages, their research is about the present. The figures about the plague are from other sources, and are mentioned only to show the extreme difference between the speed of historical pandemics and the speed of rescent pandemics.

  7. The article is interesting and it’s accessible to a wide audience, but I’d like to also see some references in the article. Has this work been published in a peer reviewed journal or in an archive? I’d like to see details.

  8. *My* suspicious yet not scientifically certified mind goes into mocking your whole comment.

    1 – RTFA
    2 – It is not a virtual simulation, they are using a bill tracking web site like the Canadian version of http://www.whereswilly.com which allows people to track where their money, specifically dollar bills go.
    3 – They use real statistics from the site.
    4 – Aren’t most statistics at least +-2% because real life != idealized equations
    5 – imho the real world usually != an ideal world

  9. My suspicious yet not scientifically certified mind goes into mocking the whole story.

    1 – it’s a simulation
    2 – in a virtual world
    3 – based on virtual parameters
    4 – using statistics with a minimum of 2% failure
    5 – imho the real world is either below or above the statistical reality

  10. we’ll see more of this kind of observation of nature in the future, where we take tons of data, like the dollar bill circulation data; run it through fast equipment like these computers here; and look at the real deal in something like real time. science will finally get to be scientific.

  11. So, I guess, I have go take a look at the latest issue of “Nature” now to find out what these “two universal parameters” of scaling laws are. A little more depth in this article would have been nice.


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