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Omaggio a JOHN GRAUNT
Tratto dall'Enciclopedia Britannica
JOHN GRAUNT, english statistician (London, April 24, 1620 - April 18, 1674)
is generally considered to be the founder of the science of demography, the statistical study of human populations.
His analysis of the vital statistics of the London populace influenced the pioneer demographic work of
his friend Sir William Petty and, even more importantly, that of Edmond Halley, the astronomer royal.
A prosperous haberdasher until his business was destroyed in the London fire of 1666, Graunt held
municipal offices and a militia command. While still active as a merchant, he began to study the death
records that had been kept by the London parishes since 1532.
Noticing that certain phenomena of death statistics appeared regularly, he was inspired to write Natural
and Political Observations . . . Made upon the Bills of Mortality (1662).
He produced four editions of this work; the third (1665) was published by the Royal Society, of which
Graunt was a charter member.
Graunt classified death rates according to the causes of death, among which he included overpopulation:
he observed that the urban death rate exceeded the rural.
He also found that although the male birth rate was higher than the female, it was offset by a greater mortality
rate for males, so that the population was divided almost evenly between the sexes. Perhaps his most important
innovation was the life table, which presented mortality in terms of survivorship.
Using only two rates of survivorship (to ages 6 and 76), derived from actual observations, he predicted the
percentage of persons that will live to each successive age and their life expectancy year by year.
Petty was able to extrapolate from mortality rates an estimate of community economic loss caused by deaths.
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