The effects of declines in mortality and fertility on rapid aging of Japanese population after the World War II.

Life expectancy at birth increased from 52.0 years to 76.9 years, and total fertility rate declined from 4.51 to 1.75 during the period 1947-1982 in Japan. In order to analyze the effects of such rapid declines in mortality and fertility on the aging of population, which is defined as increase in proportion of population 65 & over, 4 series of population projections were carried out by means of standard cohort component method. In each case, initial population applied was that of 1947, but mortality and fertility were assumed to be either constant at the level of 1947 or follow the actual trends during 1947-1982. Conditions of mortality and fertility applied are shown below. Case A: Actual trends of mortality and fertility Case B: Actual trends of mortality and constant fertility Case C: Constant mortality and actual trend of fertility Case D: Constant mortality and fertility Population projections were extended up to the year of 2082, assuming the mortality and the fertility to be constant after 1982. In each case, changes in proportion of population 65 & over and period growth rates of population 65 & over together with total population were measured. Then the contributions of mortality or fertility decline per se and interaction of both on actual and projected trend of proportion of population 65 & over were calculated separately for every 5 years. Although the effect of fertility decline appeared to play the major role in aging of population in Japan, the effect of mortality decline appeared to be far greater than it used to be in most of the European countries. It should be noted that the rapiddecline in middle and old age mortality as was experienced in post-war japan, would affect considerably the potential of population aging.