Development of a comprehensive mortality database in Japan through data linkage of population census and vital...

No official framework exists for linking the Population Census with Vital Statistics in Japan, limiting the ability to monitor health-related inequalities. We aimed to develop a new methodology for data linkage to describe sociodemographic patterns of mortality in the Japanese population.

The 2020 Population Census (n = 120,721,239) and Vital Statistics (death records: n = 2,949,946) between October 2020 and September 2022 were linked using a multi-stage deterministic linkage algorithm. Linkage variables included sex, birth year/month, residential address code (basic unit block, census block, and municipality), marital status, and age of spouse. Residential address codes (basic unit blocks: the smallest geographic unit at the Census) of death records were identified through geocoding of the exact residential address. We compared age-standardized mortality rates (ASMRs: per 100,000 person-years) before and after linkage to assess the validity of mortality. We also estimated ASMRs across multiple sociodemographic indicators, including marital status, household size, educational level, occupation, and area deprivation index (ADI).

Of the total death records, 2,253,228 (76.4%) were linked to the 2020 Census. The 2020 Japanese census-linked mortality database ultimately comprised 109,119,620 non-institutionalized Japanese individuals (90.4% of the total population) and 2,047,152 non-institutionalized death records (69.4% of total deaths). Crude all-cause mortality rates in most 5-year age categories from the database were 10-15% lower than those in the complete mortality registry without linkage; however, the difference was markedly greater in older age groups (aged ≥ 85 years), indicating less successful linkage in the age groups that had the highest mortality rates. ASMRs differed according to educational level, marital status, household size, occupation, and ADI (e.g., higher ASMRs among individuals with lower educational levels).

The new linkage framework, which incorporates detailed address information as a linkage variable, has greatly increased the included population and the completeness of linkage. This approach to developing the census-linked mortality data provides a platform for comparing population health across socioeconomic groups within Japan and Japan's health-related inequalities with those in other countries.