Public health authorities have mined medical data to spot the outbreak of infectious disease, and credit-card companies have found fraudulent credit-card purchases with the method, among other applications.

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For this reason, Dr Roberts used a technique called clustering, which has been employed extensively in other situations where census data are lacking, such as studying infectious disease in poor countries.

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Doctors would be able to use the data to gain a head start in treating and isolating outbreaks of infectious disease - an area where speed is crucial if death rates are to be minimised.

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