Population reconstitution is a method used by historical demographers

Historical demography

Historical demography is the quantitative study of human population in the past. It is concerned both with the three basic components of population change--fertility, mortality, and migration--and with population characteristics related to those components, such as marriage, socioeconomic status,...

. Using records such as church registries the size and composition of families living in a given region in a given past time is determined. This allows the identification and analysis of patterns of family formation, fertility, mortality, and migration, and of consequent trends such as population growth.