[Educational inequalities in mortality by prefectures in Japan: National census-linked mortality data, 2010-2015].

Objectives To examine a comprehensive monitoring framework for health inequalities in Japan, this study aimed to quantify educational inequalities in mortality and its regional variations, which are widely used internationally as outcome measures of health inequalities.Methods Individual data were obtained from the 2010 Population Census and Vital Statistics death records (2010-2015). We used the combination of "sex," "birth month/year," "municipality of residence," "marital status," and "age of spouse (married individuals only)" as a linkage key. Individuals with a unique "linkage key" were selected and included in the sample population. We included 7,984,451 Japanese individuals (3,992,202 men and 3,992,249 women) aged 30-79 years (9.9% of the total census population). Death records with a unique "linkage key" were linked to these records using the deterministic linkage method (five-year cumulative proportion of deaths; 5.6% for men and 2.5% for women). Inverse probability weights were calculated from the ratio of the total to sample population, using the distributions of sex, age, prefecture, educational attainment, and occupation. Weighted age-standardized mortality rates (ASMR) and ASMR ratios by educational level were calculated, and their variations by prefecture were analyzed.Results Estimated all-cause ASMRs (per 100,000 population) for men were 1,025 (95% confidence interval [CI]; 1,013-1,037) for high education (university graduation) and 1,245 (95% CI; 1,238-1,253) for middle/low education (junior/senior high school graduation). The respective values for all-cause ASMRs in women were 496 (95% CI: 485-508) and 640 (95% CI: 636-645). Estimated all-cause ASMR ratios between low/middle and high education levels were 1.21 (95% CI; 1.17-1.26) for men and 1.29 (95% CI; 1.17-1.41) for women. The ASMRs were higher for middle/low education than for high education in each prefecture; this trend was particularly pronounced among men. Additionally, no systematic differences were observed, although geographical backgrounds were considered.Conclusion Using the national census-linked mortality data, ASMR was approximately 1.2-1.3 times higher for "junior/senior high school graduates" than for "university and above graduates" in Japan. Although regional variations in the ASMR ratio were small, a more accurate mortality database must be constructed for further analysis in prefectures.