F. Causes of Population Ageing in Japan
What have then been the causes for such a rapid population ageing to take place in the future in Japan? Many people even in the journalism have made their off-the-cuff statement that recent prolongation of life expectancy is the cause for it. Indeed, as represented by Figure 7, the recent Japanese life expectancies for both males and fermales have already surpassed those of European countries such as Iceland and France which had been regarded among the highest life expectancy countries in the world. Although the above conventional view of cause of population ageing is true for Japan in the very recent years, but the fact of the matter is more complicated and the lengthening of life expectancy or mortality decline alone could not be the sole or principal factor explaining for such a substantial and rapid population ageing.
Calculations were made to decompose the difference between the percentages of the population aged 65 and over for Japan in two different years. The methodology of decomposition is Kitagawa's (1955). Some unique features of the present calculation of decomposition are that：
