4. Migration and Population Aging
Population aging in Japan has been brought due to low fertility and low mortality, as explained in the previous chapter. Analyzing the relationship between the degree of aging, or the percentage of total population in the elderly, and the degree of fertility, or total fertility rate, and that between the degree of aging and the degree of mortality, or female life expectancy at birth, among 47 prefectures being based on the data as of 1990, it was found that both of the relationships were not significant because the correlation coefficient was 0.46 for the former while it was -0.22 for the latter. On the contrary, it was recognized that correlation between the degree of aging and the degree of migration, or net migration rate for 1985-1990, was higher (0.64) than those for the correlations of againg with fertility and mortality. Therefore, it can be explained that the differences of population aging among sub-national areas such as prefectures and municipalities are caused mostly by migration.
Also, as seen in Figures 7 and 8 showing age-specific migration rates for Saitama, the youngest prefecture, and for Shimane, the eldest prefecture in the degree of population aging, among 47 prefectures, the rates of not only inmigration but also outmigration by ages are depicted in the similar pattern showing the highest at the young adult ages of 20-24 or 25-29 and lower with increasing or decreasing age except for the elderly or the child ages, which present higher than for the former or the later ages. However, the inmigration rates are higher than the outmigration rates by each ages for Saitama, while the inmigration rates are lower than the outmigration rates by almost each ages for Shimane where the outmigration rate at the ages of 20-24 presents extremely high.
