The projections were prepared by what is known as the component method which consists of the separate projections of the number of males and females in each age of the population. As a matter of convenience we project the population by time-intervals equal to the age-intervals into which it has been divided. Since the 1980 base population has been divided into quinary age groups, the projections are most easily made for five-year intervals of time which implies that at the end of the five-year period all the survivors of one age group would have moved into the next higher age group. Each cohort of the 1980 sex-age group is diminished to account for mortality with the passage of time. This step requires a set of five-year survival ratios which are deemed to represent mortality in each cohort during specific periods of time subsequent to 1980. A multiplication of the original number in each sex-age group by the relevant ratio will yield the estimated number of persons five years older at a date which is five years later, namely, 1985. A repetition of the procedure will furnish the estimated population age ten years older than those at the base date and for the ten years later.

The second step involves the estimation of the future number of children born in each five-year time-interval subsequent to the base date in order to fill in the vacuum in the first age group 0-4 at periods of time every five years later. To begin with, it is essential to formulate a set of plausible assumptions regarding the future course of fertility in terms of the gross reproduction rates with their equivalent age-specific fertility rates. Having worked out these rates, they are then utilized in conjunction with the female population in the relevant reproductive age groups to derive the estimated number of births for the various five-year periods. The number of births surviving to the end of a given five-year period can be estimated by multiplying the number of births during the period with the appropriate survival ratio.