Lambert Adolphe Jacques Quetelet was born in Ghent, Belgium, on 22 February 1796. He studied at the lycee in Ghent, where he started teaching mathematics in 1815, at the age of 19. In 1819 he moved to the athenaeum in Brussels and in the same year he completed his dissertation (De quibusdam locis geometricis, necnon de curva focal - Of some new properties of the focal distance and some other curves).
Quetelet founded several statistical journals and societies, and was especially interested in creating international cooperation among statisticians. He was among the first who attempted to apply statistics to social science, planning what he called a "social physics".
His most influential book was Sur l'homme et le developpement de ses facultes, ou Essai de Physique Sociale, published in 1835 (In English: A Treatise on Man). In it, Quetelet outlines the project of a social physics and describes his concept of the "average man" (l'homme moyen) who is characterized by the mean values of measured variables that follow a normal distribution.
Principal among these, in terms of influence over later public health agendas, was Quetelet's establishment of a simple measure for classifying peoples' weight relative to an ideal weight for their height. His proposal, the body mass index (or Quetelet index), has endured with minor variations to the present day1.
Body mass index is defined as the individual's body weight divided by the square of his height. The formulas universally used in medicine produce a unit of measure of kg/m2. BMI can also be determined using a BMI chart, which displays BMI as a function of weight (horizontal axis) and height (vertical axis) using contour lines for different values of BMI or colors for different BMI categories.