NOTE： In Column 3, the value of the percentage of the aged population at the end of the comparison period is not necessarily the same as that of the actual population, although the percentage of the aged at the beginning of the period is always the same as that of the actual population. The difference is due to many types of errors： estimated survival ratios may not perfectly represent the real process of survivorship, even though life tables used were based on the actual vital statistics data; age-specific fertility rates used may not reflect the actual situation; there may be a negligible volume of international migration which was not considered in the estimates; and there may be errors in census-tabulated figures for both the beginnings and the ends of the periods and, likewise, there may be errors in vital statistics data on fertility and mortality.
