Estimation of Socioeconomic Inequalities in Mortality in Japan Using National Census-linked Longitudinal Mortality Data

Background: We aimed to develop census-linked longitudinal mortality data for Japan and assess their validity as a new resource for estimating socioeconomic inequalities in health. Methods: Using deterministic linkage, we identified, from national censuses for 2000 and 2010 and national death records, persons and deceased persons who had unique personal identifiers (generated using sex, birth year/month, address, and marital status). For the period 2010-2015, 1,537,337 Japanese men and women aged 30-79 years (1.9% in national census) were extracted to represent the sample population. This population was weighted to adjust for confounding factors. We estimated age-standardized mortality rates (ASMRs) by education level and occupational class. The slope index of inequality (SII) and relative index inequality (RII) by educational level were calculated as inequality measures. Results: The reweighted sample population's mortality rates were somewhat higher than those of the complete registry, especially in younger age-groups and for external causes. All-cause ASMRs (per 100,000 person-years) for individuals aged 40-79 years with high, middle, and low education levels were 1,078 (95% confidence interval [CI], 1,051-1,105), 1,299 (95% CI, 1,279-1,320), and 1,670 (95% CI, 1,634-1,707) for men, and 561 (95% CI, 536-587), 601 (95% CI, 589-613), and 777 (95% CI, 745-808) for women, respectively, during 2010-2015. SII and RII by educational level increased among both sexes between 2000-2005 and 2010-2015, which indicates that mortality inequalities increased. Conclusion: The developed census-linked longitudinal mortality data provide new estimates of socioeconomic inequalities in Japan that can be triangulated with estimates obtained with other methods.