Demography (from Ancient Greek δῆμος (dêmos) ‘people, society’, and -γραφία (-graphía) ‘writing, drawing, description’) is the science concerned with the study of human populations, dealing with their amount, composition, development, and general characters, considered mainly from a quantitative point of view. Given its quantitative character, demography is based on multiple statistical indices. Modern demography was founded by German mathematician and statistician Johann Peter Süssmilch.
Demography thus studies the state of the population (amount and characteristics at a given time) and the movement of the population, that is, the changes of a biological and social nature that occur within it (births, deaths, marriages, migrations). It also studies the connections between population-related phenomena and economic and social phenomena and tends to formulate general theories about the population itself. In particular, descriptive demography and investigative demography are distinguished: the former studies the structure and evolution of populations and the latter researches the laws or regularities to which they are subject.
Historical demography studies the state and movement of the population over time while differential demography studies variations in phenomena pertaining to the population as its biological, economic and social characteristics change. The origin of demography is confused with that of statistics in that the first investigations carried out by the statistical method were concerned with phenomena pertaining to population.
Predominantly demographic in nature were in fact the researches of J. Graunt, W. Petty and the other followers of Political Arithmetic (by which Graunt had referred to the science later defined by C. Davenant as “the art of reasoning by means of figures about things pertaining to government”), from which began both statistics as a complex of methods and demography as an autonomous science in the modern sense of the term. For example, Graunt, who tried to determine the number of inhabitants of London and estimate their distribution by sex and age, also constructed the first mortality table in history. The year in which his work with the results of his investigations was published, 1662, is traditionally considered the birth date of demography. The first real treatise on demography, however, is considered The Divine Order of the Changes of Mankind, Demonstrated by Birth, Death and the Reproduction thereof by J. P. Süssmilch, the first edition of which was published in 1741.