QUETELET, ADOLPHE

(1796–1874)

Born in Ghent, Belgium, mathematician and demographer Adolphe Quetelet earned a doctorate in mathematics at the age of twenty-three and was elected, one year later, to the Académie royale des sciences et belles-lettres. The Belgian academy became the central place from which Quetelet directed most of his activities for the rest of his life. He worked in a variety of disciplines such as astronomy, meteorology, physical geography, development psychology, demography, and statistics. Quetelet's work was profoundly influenced by early probability theory. From astronomer and mathematician Pierre-Simon Laplace (1749–1827), Quetelet learned that measurement errors are normally distributed around the true value; this information allowed him to detect systematic errors in early social science data. His notion of l'homme moyen also stems from Laplace's theory. However, Quetelet was never exclusively preoccupied by averages, and whenever possible he presented complete distributions. One of his contributions to demography is his presentation of age-specific rates for vital events or for other phenomena (e.g., crime), and his construction of time series. In fact, the materials brought together in his Physique Sociale (1835) mark the beginning of the statistical study of the life cycle. Quetelet's interpretation of population distributions of social characteristics announced the advent of sociology as a new science, according to which the entity called "society" could be studied and analyzed with objective methods. In contrast to philosopher Auguste Comte (1798–1857), Quetelet never developed a general plan for this new discipline, but his influence on sociology remained strong throughout the nineteenth century, as is evidenced in the work of French sociologist Émile Durkheim (1858–1917).

Quetelet's contribution to demography started in the 1820s. Together with E. Smits, he noted, like several others before him (e.g., French military engineer Sébastien Vauban [1633–1707] and German demographer Johann Peter Süssmilch [1707–1767]) that the numbers and age distributions of vital events in the Low Countries showed a remarkable degree of stability over time. In Physique Sociale, Quetelet argued that only major disturbances were capable of producing temporary distortions. By contrast, les causes constantes would re-establish the dominant pattern. This is a view similar to that of the homeostatic demographic regime of the economist T. R. Malthus.

Quetelet's other contributions to demography deal respectively with census taking and life table construction. These two areas were intimately related since no direct measurement of probabilities of dying (i.e., the q_x-function of a life table) was available at that time. Hence, like all other investigators before him, Quetelet depended on the stationarity assumption that permitted the linkage of ved age structures to the L_x-function (numbers of person-years lived in an age interval). Quetelet explicitly discussed the properties of stationary populations, and showed that the hypothesis of constant mortality could be relaxed. In fact, he was on the way to showing that there is a neutral pattern of mortality decline (i.e., a reduction in age-specific death rates which does not alter the shape of the population age distribution). (For the proof, see A. J. Coale, 1972: 33–36.) Quetelet was never able to develop a model for a stable population with a constant growth rate different from zero. He also failed to recognize the significance of the logistic curve developed by one of his younger colleagues, Belgian mathematician and demographer Pierre-François Verhulst (1804–1849). In actual practice, Quetelet remained a master of comparative statics rather than of social dynamics.

Quetelet did not comment on the numerous social developments in Belgium, which began in the 1860s. After suffering a stroke in 1855, his scientific innovativeness ended. However, until his death in 1874, Quetelet continued to inspire statistical applications in other many fields, and to promote international comparability of statistical information. In the words of mathematician Alain Desrosières, "Quetelet was the orchestra conductor of nineteenth century statistics" (Derosières, p. 95).

BIBLIOGRAPHY

SELECTED WORKS BY ADOLPHE QUETELET.

Quetelet, Adolphe. 1835. Sur l'homme et le développement de ses facultés ou essai de physique sociale. Paris: Editions Bachelier. English transl.: A Treatise on Man and the Development of His Faculties. Edinburgh: Chambers, 1842.

——. 1848. Du système social et des lois qui le régissent. Paris: Guillaumin et Cie.

——1849. "Nouvelles tables de mortalité pour la Belgique." Bulletin de la Commission Centrale de Statistique 4: 1–22.

SELECTED WORKS ABOUT ADOLPHE QUETELET.

Académie Royale de la Belgique. 1997. Actualité et universalité de la pensée scientifique d'Adolphe Quetelet. Classe des Sciences, Actes du Colloque 24–25.10.96, Brussels, Belgium.

Coale, Ansley J. 1972. The Growth and Structure of Human Populations–A Mathematical Investigation. Princeton, NJ: Princeton University Press.

Desrosières, A. 1993. La politique des grands nombres–Histoire de la raison statistique. Paris: Editions La Decouverte. English edition: The Politics of Large Numbers: A History of Statistical Reasoning. Cambridge, MA: Harvard University Press. 1998.

Lesthaeghe, R. 2001. "Quetelet, Adolphe (1796–1874)." In Encyclopedia of the Social and Behavioural Sciences. Oxford: Elsevier Science Ltd.