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 its 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 1078 (95% confidence interval: 1051-1105), 1299 (1279-1320), and 1670 (1634-1707) for men, and 561 (536-587), 601 (589-613), and 777 (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 mortality inequalities increased.

CONCLUSIONS

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.