Influences of mortality from main causes of death on life expectancy. \ An observation for the past 25 years, 1950-1975, in Japan \ Takao SHIGEMATSU* and Zenji NANJO** With the Keyfitz-Nanjo method an observation was made on the data of Japanese longevity and mortality for the past 25 years from 1950 to 1975. Prolongations of longevity by mortality decline of selected 12 causes for five quinquenial years were calculated. As an application of the method, estimations of length of life at birth in 1980 and of effects of mortality decline in a specified age group were also made. The results were summerised as follows. (1) The calculated prolongations were close to the observed ones and the results were well conformed to the observed relations of past mortality and longevity in Japan. The method provide a good tool to evaluate the effect of certain death cause to expectation of life. (2) Rapid decline of infectious disease mortalities played a main role on the large prolongation of longevity in 1950's, 65% of total prolongation for male and 59% for female in the period of 1950-1955, but their influences decreased with the mortality decline, 49%, 43% in 1960-1965, and 17%, 33% in 1970-1975 for male and female respectively. (3) Influences of adult diseases were gradually increasing since 1960's with the aging of the population and in the last 5 year period, 1970-1975, cerebrovascular diseases became the largest contributor to the longevity prolongation, 26% for male and 24% for female and influences of 5 adult diseases accounted for 34% and 40% of total prolongation for male and female respectively. 4) Influences of remaining causes, senility and external causes varied from time to time reflecting socio-economic conditions in Japan. 5) Although estimated life expectancy in 1980 was wide of the mark because Japanese longevity in 1980 was shortened due to unexpected reasons, the method gave reasonable estimates and seemed to be available for estimation of longevity in the near future. Estimation of the effects of mortality decline for age 40-65 would be an useful index in diesease control programme.

Table 1 Averge Length of Life at Birth in Japan, 1947-1979 Source: Complete life tables, Ministry of Health & Welfare * Complete life table, Mizushima, H, et al. # Abridged life table, Ministry of Health & Welfare

Table 2 Percent of Total Deaths for 10 Leading Causes of Death, 1950, 196 and 1975 Source: Vital Statistics in Japan 1950, 1965, 1975

Fig.1 Crude mortality rates for selected causes of death by sex, 1950-1975 Source: Vital Sltatistics Report 1950-1975

Table 3 Age-adjusted Death Rates for Selected Causes of Death in Japan, 1950-1975 Standard population: 1935 census population of all Japan by sex Source: Standardized Death Rates for Main Causes of Death, 1975

Percent decrease was calculated from age-adjusted death rates Negative sigh indicates increase in mortality

Table 5 Prolongation of Life Expectancy Resulted from Observed Decrease of Selected Causes of Death and Their Percent of Total Prolongation in Japan, 1950-1975 Negative sign means decrease of life expectancy due to increase of mortality for the cause

Table 6 Expected Prolongation of Life Expectancy When a Certain Cause of Death Was Completely Eliminated, 1975, Japan Source: 1975 Prefecture Life Tables in Japan. Health and Welfare Stat. Assoc. 1977 Table 7 Estimated Expectation of Life at Birth in 1980

Table 8 Estimated Prolongation of Length of Life at Birth When Mortalities from 3 Adult Diseases for Age 40-69 Were Decreased by a Given Rate, 1978

Greville, T.N.E.: On the Formula for the L- Function in a Special Mortality Table Eliminating a Given Cause of Death. ; Transactions of the Society of Actuaries 6 (1), 1-5, 1954 Keyfitz, N.: What Difference Would It Make If Cancer Were Eradicated? An Examination of The Taeuber Paradox.; Demography 14, 411-418, 1977 Nanjo, Z.: A Simple Method of Measuring the Increase of Life Expectancy When A Fixed Percent of Deaths From Certain Causes Are Eliminated.:IIASA Collaborative Paper, CP- 80-35, 1980

Appendix I Coefficients Cix to Calculate Prolongation of Expectation of Life at Birth in 1978, Japan

Appendix U Coefficients Ctx to Calculculate Prolongation of Expectation of Life at Age 65 in 1978, Japan