Population change

Population growth is usually referred to as “population change” – since empirical values as well as theoretical ones may be positive, zero, or negative. It is measured as “the difference between the sizes of a population at different dates.” “Population” may refer to the population of a country, a region, or other subdivision of a country or a proper subset of such a population (e.g., “illegal immigrants in California”). “Different dates” are usually at a distance of a (calendar) year but may also be at monthly intervals or some other interval (such as a decade or an intercensal period).

Population growth may be measured in absolute values or as a relative measure. In the former case, we subtract the population count at the earlier of two dates from the population count at the later date. In the latter case, we divide the difference thus obtained by the population count at the earlier date. Such a relative rate may be converted into a percentage...