Great Plains Studies, Center for
Date of this Version
Fall 2002
Citation
Great Plains Quarterly Vol. 22, No. 4, Fall 2002, pp. 245-58.
Abstract
Students of population and regional studies are familiar with the demographic "accounting" equation,
Population t+x = Population t + Births x
-Deaths x + Immigration x
- Emigration x
In other words, the size of the population at time t + x is equal to the population at time t plus the births, minus the deaths, plus the immigrants, minus the emigrants, during the interval of time x. This simple formula can be used to derive a variety of rates and statistics describing population change. The equation's main application is to describe short-term change in a population in terms of its various components.
Viewed another way, population size is a chain of growth components linked by generation:
Population = Number of immigrants
+ Births to immigrants
+ Births to children of immigrants + ...
- (Sum of deaths and emigration).
In this view, everyone is either an immigrant or a child (grandchild, great-grandchild, ... ) of an immigrant, provided the reckoning is extended backward in time to the arrival of the very first humans to live in a place. As the earliest immigrants die or leave the region, they are replaced by their children, then by their grandchildren, and so on. This type of accounting equation has as many terms as there are generations and groups of people. Although we sometimes refer to the earliest people in an area as "native," even groups inhabiting an area for a very long time are descended from ancestors who came from some other place.
These definitions can be applied to the study of population in the Great Plains or any other region. The migration-based approach to studying population change is especially relevant in the Plains because of the large volume of both in- and out-migration that has characterized the region's history. Equations (1) and (2) represent two distinct approaches to the study of migration. In equation (1) migration is a process of updating the population. In every time period, arrivals are added to the total and departures are subtracted. Time is chronological and calendrical. The approach is suited for use in population studies based on census data or on other regularly collected statistics. In equation (2), time is generational, with contributions to population size being made by successive generations of immigrants and their descendants. Censuses do not record populations in this way, however, so equation (2) is of limited usefulness in regional population studies.
Comments
Copyright 2002 by the Center for Great Plains Studies, University of Nebraska-Lincoln