Reconstruction of Japanese Population by Birth Year through Vital Statistics Accumulation and Comparison with Static Statistics: Based on Mortality Structure Estimation for 1944/45

This study reconstructs Japanese population data by birth cohort using vital statistics (births minus deaths) over approximately 150 years from 1872 to 2023, comparing it with static statistics from census data. A critical challenge addressed is the absence of age-specific mortality data for 1944-45 during World War II. Through estimation using surrounding static statistics, the study reveals 3.76 million excess deaths during these two years, with particularly high mortality among men around age 25 in 1945 (born circa 1920). Incorporating these estimates, the comparison between dynamically accumulated population and the 2020 census (including overseas Japanese) shows the former exceeds the latter by only 0.3%. Despite institutional disconnection between vital and static statistics systems, their differences remain within acceptable ranges. The research emphasizes that amid concerns about statistical deterioration in the big data era, efforts should focus not only on improving individual statistics but also on enhancing coordination and utilization of existing multiple statistical systems.