Influences of mortality from main causes of death on life expectancy.

—An observation for the past 25 years, 1950-1975, in Japan—

Abstract

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.