Document Type


Publication Date

Spring 5-1983


A cohort component II technique is used to project the 1980 population by age and sex for each of Tennessee's 95 counties to 1990 and 2000. The name of the technique implies the methodology. "Cohort" refers to specific age-sex groups (e.g., females 10-14 in 1980) that first are hypothetically aged 10 years to 1990, and second, aged 10 more years to 2000; "component" refers to the rates of fertility, mortality and migration assumed to be in effect over the projection period. To obtain the projected population, each age-sex group is increased or decreased by applying appropriate age-sex specific rates of fertility, mortality and net migration.

The components of change include observed fertility and mortality rates as well as estimated net migration rates for the initial population to be projected. Variations in the component rates provide the basis for a series of forecasts. Use of a projection series acknowledges the difficulty in predicting actual levels of future vital events and their cumulative effects in determining a future population size. Series projections provide a range of reasonable forecasts based upon variations in the component rates, they may be seen as responses to questions such as: "How large will our population be in 10 years if there are no changes in levels of births, deaths, or migration? In 20 years? If migration decreases? If fertility deer-eases?'' Component rates thus become major assumptions in the projection process.

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