Drunkard's Walk - Leonard Mlodinow [77]
A big step in that transformation of views came in the sixteenth century, when the lord mayor of London ordered the compilation of weekly “bills of mortality” to account for the christenings and burials recorded by parish clerks. For decades the bills were compiled sporadically, but in 1603, one of the worst years of the plague, the city instituted a weekly tally. Theorists on the Continent turned up their noses at the data-laden mortality bills as peculiarly English and of little use. But to one peculiar Englishman, a shopkeeper named John Graunt, the tallies told a gripping tale.7
Graunt and his friend William Petty have been called the founders of statistics, a field sometimes considered lowbrow by those in pure mathematics owing to its focus on mundane practical issues, and in that sense Graunt in particular makes a fitting founder. For unlike some of the amateurs who developed probability—Cardano the doctor, Fermat the jurist, or Bayes the clergyman—Graunt was a seller of common notions: buttons, thread, needles, and other small items used in a household. But Graunt wasn’t just a button salesman; he was a wealthy button salesman, and his wealth afforded him the leisure to pursue interests having nothing to do with implements for holding garments together. It also enabled him to befriend some of the greatest intellectuals of his day, including Petty.
One inference Graunt gleaned from the mortality bills concerned the number of people who starved to death. In 1665 that number was reported to be 45, only about double the number who died from execution. In contrast, 4,808 were reported to have died from consumption, 1,929 from “spotted fever and purples,” 2,614 from “teeth and worms,” and 68,596 from the plague. Why, when London was “teeming with beggars,” did so few starve? Graunt concluded that the populace must be feeding the hungry. And so he proposed instead that the state provide the food, thereby costing society nothing while ridding seventeenth-century London streets of their equivalent of panhandlers and squeegee men. Graunt also weighed in on the two leading theories of how the plague is spread. One theory held that the illness was transmitted by foul air; the other, that it was transmitted from person to person. Graunt looked at the week-to-week records of deaths and concluded that the fluctuations in the data were too great to be random, as he expected they would be if the person-to-person theory were correct. On the other hand, since weather varies erratically week by week, he considered the fluctuating data to be consistent with the foul-air theory. As it turned out, London was not ready for soup kitchens, and Londoners would have fared better if they had avoided ugly rats rather than foul air, but Graunt’s great discoveries lay not in his conclusions. They lay instead in his realization that statistics can provide insights into the system from which the statistics are derived.
Petty’s work is sometimes considered a harbinger of classical economics.8 Believing that the strength of the state depends on, and is reflected by, the number and character of its subjects, Petty employed statistical reasoning to analyze national issues. Typically his analyses were made from the point of view of the sovereign and treated members of society as objects to be manipulated at will. Regarding the plague, he pointed out that money should be spent on prevention because, in saving lives, the realm would preserve part of the considerable