John Graunt, 1620-1675

English politicial arithmetician, father of demographic and social statistics. 

John Graunt, the son of a Hampshire draper, followed his father's profession and became a London haberdasher, pursuing his own education and intellectual interests in his spare time.  Graunt's business prospered and it was partly through his influence in the London guilds that his good friend, William Petty, was appointed to the chair of music at Gresham College in 1650.  Petty would return the favor later by easing Graunt's entry into the Royal Society. Graunt's business was ruined by the Great Fire of London in 1666 and he compounded his difficulties by converting to Catholicism late in life.  

John Graunt's principle claim to fame is his authorship of the ground-breaking Natural and Political Observations...upon the Bills of Mortality, published in 1662.  Being a relative unknown, 'John Graunt' was widely assumed to be a pseudonym of William Petty and many historians since have perpetuated that misattribution.  But there is now little doubt that Graunt was the real author, although the project might very well have been proposed and outlined to him by Petty, and it is also possible that Petty may have had a hand in composing the preface and conclusion.

Graunt endeavored to provide reliable estimates on the basis of scant data of mortality and birth rates, sex ratios, migration, life expectancy and causes of death.  His principle innovation was his use of large numbers logic, that is, the argument (then novel) that while all these things are mere chance in an individual, they are reliably steady in the aggregate. Moreover, Graunt showed, changes in the aggregate numbers can be scientifically explained, and can be the basis of useful predictions. 

Among the more interesting insights gleaned from Graunt's work was the demonstration that death rates in London exceeded birth rates, and yet building rates were increasing, "It is therefore certain that London is supplied with People from out of the Countrey" (p.41-42).  A simple observation that could long be gleaned from watching the streaming vagabonds migrating from the country, to be sure, but never one quite backed up before by the power of data.

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