In 1854 John Snow correctly identified the cause of a cholera outbreak in London. It was a contaminated water pump. He then struggled, and eventually succeeded, in persuading the city authorities to take the handle off the pump. It was a historic achievement in the history of public health. The same year, England's august Cholera Inquiry Commission published a 629-page report on the causes of cholera. Their conclusion: the culprit was "bad air"—the noxious emissions that were associated with poor neighborhoods. They had 629 pages of data, and it lead them to a wrong conclusion.