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Delivered-To: clips@philodox.com
Date: Thu, 26 Jan 2006 12:02:32 -0500
To: Philodox Clips List
From: "R. A. Hettinga"
Subject: [Clips] Banknote tracking helps model spread of disease
Reply-To: rah@philodox.com
Sender: clips-bounces@philodox.com
http://www.newscientist.com/article.ns?id=dn8636&print=true
New Scientist
Banknote tracking helps model spread of disease
* 18:15 25 January 2006
* NewScientist.com news service
* Will Knight
Tracking the movements of hundreds of thousands of banknotes across the US
could provide scientists with a vital new tool to help combat the spread of
deadly infectious diseases like bird flu.
Modern transport has transformed the speed at which epidemics can spread,
enabling disease to rip through populations and leap across continents at
frightening speed.
However, scientists possess few mathematical models to help them understand
these movements and how this might govern the global spread of disease. To
a large degree, this is because tracking the movements of so many people
over such a large area is next to impossible.
But now physicists from the Max Planck Institute in Gvttingen, Germany, and
the University of Santa Barbara, California, US, have developed a model to
explain these movements, based on the tracked movements of US banknotes.
Dirk Brockmann and colleagues used an online project called
www.wheresgeorge.com (George Washington's image is on the $1 bill) to track
the movements of dollar bills by serial number. Visitors to the site enter
the serial number of banknotes in their possession and can see where else
the note may have been.
The team tracked 464,670 dollar bills across the US using 1,033,095
individual reports. The fact the notes are carried by people suggests it is
a good way of modelling other things that people may carry, including
disease.
Piggy bank
The researchers noticed that the bills' move according to two mathematical
rules, each known as a power law. One describes the distance travelled in
each step of the journey, the other the length of time spent between
journeys.
While most notes travel a short distance each time, there is a slim
probability that it will leap a very long distance - perhaps carried from
one side of the US to the other in the wallet of a passenger taking a
flight. Secondly, while some notes move on quickly, there is a fair chance
that it will remain in one place for a long period - for instance stuffed
into a child's piggy bank.
Although the movements of individual bills remain unpredictable, the
mathematical rules make it possible to calculate the probability that a
bill will have travelled a certain distance over a certain amount of time.
"What's triggering this is our behaviour," Brockmann told New Scientist.
"That is what you need if you want to build quantitative models for the
spread of disease."
Very, very important
Brockmann admits that the movement of money may not perfectly mirror that
of people. For one thing, he says, it may be that only certain types of
people are interested in seeing where their bills have been and entering
that on www.wheresgeorge.com. However, he says comparing the model to
publicly available information on passenger flights and road travel
suggests that it is accurate.
Luis Amaral at Northwestern University, US, believes the study could indeed
prove very useful to epidemiologists. "Understanding the way people move
can be very, very important for developing strategies for fighting
disease," he told New Scientist. "It seems like a very cool study."
But Amaral also says that the comparison between banknotes and disease is
far from perfect. "Banknotes do not reproduce like a disease," he notes.
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R. A. Hettinga
The Internet Bearer Underwriting Corporation http://www.ibuc.com/
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'
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R. A. Hettinga
The Internet Bearer Underwriting Corporation http://www.ibuc.com/
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'