Drunkard's Walk - Leonard Mlodinow [78]
If, as Petty believed, the size and growth of a population reflect the quality of its government, then the lack of a good method for measuring the size of a population made the assessment of its government difficult. Graunt’s most famous calculations addressed that issue—in particular the population of London. From the bills of mortality, Graunt knew the number of births. Since he had a rough idea of the fertility rate, he could infer how many women were of childbearing age. That datum allowed him to guess the total number of families and, using his own observations of the mean size of a London family, thereby estimate the city’s population. He came up with 384,000—previously it was believed to be 2 million. Graunt also raised eyebrows by showing that much of the growth of the city was due to immigration from outlying areas, not to the slower method of procreation, and that despite the horrors of the plague, the decrease in population due to even the worst epidemic was always made up within two years. In addition, Graunt is generally credited with publishing the first “life table,” a systematic arrangement of life-expectancy data that today is widely employed by organizations—from life insurance companies to the World Health Organization—that are interested in knowing how long people live. A life table displays how many people, in a group of 100, can be expected to survive to any given age. To Graunt’s data (the column in the table below labeled “London, 1662”), I’ve added columns exhibiting the same data for a few countries today.10
Graunt’s life table extended
In 1662, Graunt published his analyses in Natural and Political Observations…upon the Bills of Mortality. The book met with acclaim. A year later Graunt was elected to the Royal Society. Then, in 1666, the Great Fire of London, which burned down a large part of the city, destroyed his business. To add insult to injury, he was accused of helping to cause the destruction by giving instructions to halt the water supply just before the fire started. In truth he had no affiliation with the water company until after the fire. Still, after that episode, Graunt’s name disappeared from the books of the Royal Society. Graunt died of jaundice a few years later.
Largely because of Graunt’s work, in 1667 the French fell in line with the British and revised their legal code to enable surveys like the bills of mortality. Other European countries followed suit. By the nineteenth century, statisticians all over Europe were up to their elbows in government records such as census data—“an avalanche of numbers.”11 Graunt’s legacy was to demonstrate that inferences about a population as a whole could be made by carefully examining a limited sample of data. But though Graunt and others made valiant efforts to learn from the data through the application of simple logic, most of the data’s secrets awaited the development of the tools created by Gauss, Laplace, and others in the nineteenth and early twentieth centuries.
THE TERM statistics entered the English language from the German word Statistik through a 1770 translation of the book Bielfield’s Elementary Universal Education, which stated that “the science that is called statistics teaches us what is the political arrangement of all the modern states in the known world.”12 By 1828 the subject had evolved such that Noah Webster