The Belgian polymath Lambert Adolphe Jacques Quetelet (1796–1874) pioneered social statistics. Applying his training in mathematics to the physical and psychological dimensions of individuals, he identified the 'average man' as characterised by the mean values of measured variables that follow a normal distribution. He believed that comparing the features of individuals against this average would allow scientists to better explore the processes that determine normal and abnormal qualities. Quetelet's methods influenced many, among them Florence Nightingale, and his simple measure for classifying a person's weight, dividing it by the square of their height, is widely known as the body mass index. First published in French in 1835 and reissued here in the 1842 English translation, this is his most influential work and includes a new preface that succinctly states his aim to be 'the analysis of normal man through his actions and of intellectual man through his productions'.