A baseline projection assumes people have the right to migrate where they choose and no major natural catastrophes or war will befall the state or the nation. A cohort-component method traces people born in a given year through their lives. As each year passes, cohorts change due to the mortality and migration assumptions. New cohorts are formed by applying the fertility assumptions to the women of childbearing age. The primary sources of special populations are prisons, colleges, and military installations.
Special populations display very different demographic characteristics and behavior.
In counties where special populations represented a significant proportion of the total population, they were removed from the base and projected separately. For prison and military populations, the determination was made based on an examination of sex ratios and, to a lesser extent, the age structure. College adjustments were based on an examination of age structure. Forecasts from the Department of Corrections were used to determine the timing and capacity of new facilities. Information from individual military bases as well as the Pentagon was used to project the population effects of base closures and realignments.