Researchers looking to model the spread of infectious diseases are being helped by an amateur website that tracks banknotes.
Where's George? was set up in 1998 as a bit of fun and allowed users to register the serial numbers of their dollar bills and track them around the country as they were spent. The site is currently tracking over 76 million bank notes.
A study published in Nature entitled The Scaling laws of Human Travel said that researchers at the Max-Planck Institute for Dynamics and Self-Organisation found this kind of data valuable as they tried to model the spread of infectious diseases.
Because an exchange of cash requires human contact the data on currency movements has proved very useful in researching infection transmission.
"Human travel, for example, is responsible for the geographical spread of human infectious disease," the team wrote.
"In light of increasing international trade, intensified human mobility and the imminent threat of an influenza epidemic, knowledge of the dynamic and statistical properties of human travel is of fundamental importance.
"We have developed a solid and quantitative assessment of human travelling statistics by analysing the circulation of bank notes in the US."
A similar scheme to track euro bank notes can be found here.
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