The methodology used in this set of population projections is similar to that used by Jacobsen and Hastings (1983); thus, our discussion draws heavily from the earlier report.
The cohort component II technique as outlined by Irwin (U.S. Bureau of the Census, 1977) is used to project the 1980 population by age, sex, and race for the state of Tennessee and each of the 95 counties to 1990 and 2000. This technique is most typically used when projecting national populations, states, or counties. For smaller civil divisions it is too unwieldy as a strategy.
The narrative the strategy followed. A "cohort" is an aggregate of individuals who experience the same event in the same tine interim. For instance, all people corn in 1980 are refers of the birth cohort of 1980. "Component" refers to the rates of fertility, mortality, and migration assumed to be in effect during the projection period. To project a population then, an initial population estimate or count is obtained, in this case, the 1980 census count. Each age-sex group is aged 10 years to 1990 and subject to losses and gains. Losses and gains are generated by applying the appropriate age-sex specific rates of fertility, mortality, and migration against the population age-sex distribution.
These components of change include observed fertility and mortality rates as well as estimated net migration rates for the initial population to be projected.
Clevenger, William F. and Hastings, Donald W., "Tennessee Population Projections: 1990-2000" (1985). Tennessee State Data Center.