Demography 101: Flow, Stock, and the Wall
By David North on January 28, 2019
In the first week of Demography 101 one learns that there are two basic sets of population measures, the stock and the net flow.
Stock counts or estimates the total number of individuals within a given area at a given time, as does a census.
Net flows deal with population movements; usually, the formula for a given amount of time is:
(inward migration + births) - (outward migration + deaths) = net flow
Generally, unless the net inward flow is caused by an advancing army, the impact on the general population of the stock of a particular population is more important than the impact of the inward flows, as the flow usually represents a much smaller number than the stock.
https://cis.org/North/Demography-101-Flow-Stock-and-Wall
