Cohort-component population projections (cont.)

Overview

The steps of a cohort-component projection are:

• to project every age cohort for one projection interval at a time
• to calculate the births during this interval and add in the newly-born children
• to adjust for migration

before moving on to repeat the procedure to project the population to the end of the next interval.

To project a population in intervals of n years, one uses data on n-year age groups. Thus, populations are usually projected either one-year at a time, using data on single-year age groups, or by five-years at a time, using data on five-year age groups.

This session illustrates the cohort-component method with projections base on five-year projection intervals and age groups. With appropriate computer software to do the calculations, however, only slightly more effort is required to project a population by one year at a time.