Adolphe Quetelet (1796-1874)

Adolphe Quetelet was one of the most influential social statisticians of the nineteenth century. His applications of statistical reasoning to social phenomena profoundly influenced the course of European social science.

Quetelet was born in Ghent, Belgium on February 22, 1796. He received a doctorate of science in 1819 from the University of Ghent. He taught mathematics in Brussels after 1819 and founded and directed the Royal Observatory. Quetelet had studied astronomy and probability for three months in Paris in 1824. He learned astronomy from Arago and Bouvard and the theory of probability from Joseph Fourier and Pierre Laplace. Here he learned how to run the observatory. Quetelet gave special attention t o the meteorological functions of his observatory.

One science was not enough, however, for Quetelet. Starting around 1830, he became heavily involved in statistics and sociology. Quetelet was convinced that probability influenced the course of human affairs more so than earlier generations had a nd more so than his contemporaries did. Astronomers had used the law of error to gain accurate measurement of phenomena in the physical world. Quetelet believed the law of error could be applied human beings. If the phenomena analyzed were part of huma n nature, Quetelet believed that it was possible to determine the average physical and intellectual features of a population. Through gathering the "facts of life," the behavior of individuals could be assessed against how an "average man& quot; would normally behave. He believed it possible to identify the underlying regularities for both normal and abnormal behavior. "Average man" could be known from graphically arraying the facts of life as bell shaped curves.

Quetelet had come to be known as the champion of a new science, dedicated to mapping the normal physical and moral characteristics. Quetelet called it social mechanics. He published a detailed account of the new science in 1835 which he titled A T reatise on Man, and the Development of His Faculties. This was a lengthy account of the influence of probability over human affairs.

Quetelet thought more of "average" physical and mental qualities as real properties of particular people or races awaiting discovery and not just abstract concepts. Quetelet helped give cognitive strength to ideas of racial differences in ni neteenth century European thought. His conception of "average man" is the central value about which measurements of a human trait are grouped according to the normal curve. The "average man" began as a simple way of summarizing some characteristic of a population, but in some of Quetelet’s later work, "average man" is presented as an ideal type, as if nature were shooting at the "average man" as a target and deviations from this target were errors. Cournot and ot hers criticized the concept. An individual average in all dimensions might not even be biologically feasible, they argued.

In 1846 he published a book on probability and social science that demonstrated as diverse a collection of human measurements as the heights of French conscripts and the chest circumferences of Scottish soldiers could be taken as approximately normally distributed. The use of the normal curve in areas so far from astronomy and geodesy had a powerful influence on Francis Galton and may have influenced James Clark Maxwell in his formulating the kinetic theory of gases.

Quetelet believed that if the investigator took care to ensure that they had obtained accurate measurements of individuals belonging to a particular race or nationality, it would be possible to determine any unknown physical or intellectual aspect of t he population under investigation.

Quetelet was the first to use the normal curve other than as an error law. His studies of the numerical consistency of crimes stimulated discussion of free will versus social determinism. He collected and analyzed statistics on crime, mortality, etc. for the government and devised improvements in census taking.

The Quetelet index is the internationally used measure of obesity. The Quetelet index is:

QI = weight in kilograms / (height in meters)²

If QI > 30 then the person is officially obese.

Quetelet organized the first international statistics conference in 1853. He was instrumental in the forming of the Statistical Society of London, the International Statistics Congresses, and the Statistical Section of the British Association for the Advancement of Science. He was the fist foreign member of the American Statistical Association. The historian of science George Sarton called him the "patriarch of statistics."

http://www.cimm.jcu.edu.au/hist/stats/quet/index.htm

http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Quetelet.html

Stigler, Stephen M. "Adolphe Quetelet." Encyclopedia of Statistical Sciences. New York:

John Wiley & Sons. 1986.