his coworkers. The paper described statistical laws of human travel in the United States, and developed a mathematical model of the spread of infectious disease resulting from such travel. The article was published in the January 26, 2006, issue of the journal Nature. Researchers found that 57% of the nearly half a million dollar bills studied traveled between over approximately nine months in the United States. A short clip of a Brockmann's presentation on the subject from the IdeaFestival has been posted on YouTube. In 2009 "Where's George?" data have been used to attempt to predict the rapidity and pattern of projected spread of the 2009 swine flu pandemic. See also BookCrossing -- Service to track used book circulation Currency bill tracking EuroBillTracker The Money Tracker – the site's Australian counterpart Twenty Bucks – 1993 film about the fictional travels of a $20 bill Where's Willy? – the site's Canadian counterpart References External links Directory of Where's George related pages – a wealth of information regarding Where's George WG? Virtual Museum – a collection of marked bill images. WG? Videos on YouTube – Videos relating to Where's George by Brian Galbreath. The Dollar Project (1986–1988) – an earlier art project involving tracking stamped bills. Internet object tracking Internet properties established in 1998 Numismatics Paper money of the United States