Lambert-Adolphe-Jacques Quetelet

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Lambert-Adolphe-Jacques Quetelet


Belgian Statistician, Astronomer and Meteorologist

Adolphe Quetelet envisioned a new scientific discipline that he called "social physics." It is one of the precursors of sociology. Social physics combines statistical enumeration with the analytical tools of probability theory. He coined the term "average man," a fictitious person with average build and average mental characteristics. To coordinate the collection of statistical data Quetelet organized international statistical congresses.

Lambert-Adolphe-Jacques Quetelet was born in 1796 in Ghent, in the French speaking part of Belgium. Just before his birth Belgium had been annexed by France, and when French leader Napoleon Bonaparte was defeated in 1816 the Allies joined Belgium with the Netherlands to form a stronger buffer against future French ambitions. All during his early life Quetelet would strive for Belgium to become an autonomous nation.

Quetelet's dissertation was in geometry. In 1823 he traveled to Paris to seek advice for his plan to build an observatory for astronomy, meteorology, and geomagnetism in Brussels. There he met famous scientists such as Pierre Laplace (1749-1827) and Siméon Poisson 1781-1840(). Through these contacts Quetelet became interested in statistics and probability theory.

In 1826 he published his first statistical study, a birth- and death-statistics for the city of Brussels to form a basis for a reliable life insurance. In 1831, in a study on crime statistics, he introduced his famous concept of "average man." The "average man" is a fictitious being for whom everything happens according to the average results obtained for the whole society. Just as stable mortality statistics proved that the average man had a stable probability to die, Quetelet argued, he had also a propensity to commit a crime: "Thus we pass from one year to another with the sad perspective of seeing the same crimes reproduced in the same order and calling down the same punishments in the same proportions.... There is a budget which we pay with a frightful regularity; it is that of prisons, chains, and the scaffold."

These ideas obtained wide circulation in his famous treatise of 1835, "A Treatise on Man and the Development of his Faculties," published in Paris. This work was translated into many languages. It is subtitled "An Essay on Social Physics"; in it the average man is on the one hand an analog of averaging large numbers of observations to find planetary positions and on the other an expression of societal forces. According to Quetelet "society includes within itself the germs of all the crimes committed.... It is the social state, which prepares these crimes, and the criminal is merely the instrument to execute them."

These ideas led to accusations of fatalism and materialism, and all over the Western world heated discussions were held to decide whether regular crime statistics are compatible with the assumption that people have a free will.

For the remainder of his scientific career Quetelet became the untiring promoter of international cooperation in the collection of statistical data. He was one of the first foreign members of the American Statistical Association founded in 1839, and in 1853 Quetelet organized the International Congress of Statistics. Its goal was to introduce unity in the official statistical investigations of the participating countries to make the results comparable. Eight more of these congresses were to follow. Looking back, Quetelet claimed later that statistics had been as equally important for the nineteenth century as the metric system, the steam engine, and photography.

Quetelet's funeral was a gathering of scientists and politicians from all over the world. A statue of him was erected in 1880. It shows him seated in an armchair, the fingers of his left hand spread out on a nearby globe, and his head raised as he peers into the secrets of space.