Municipal socioeconomic status and mortality in Japan: sex and age differences, and trends in 1973–1998

The purpose of this study was to examine the sex and age differences and the time trends in the association between municipal socioeconomic status (SES) and all-cause mortality across Japan from 1973 to 1998. Sex-specific mortality of municipalities (N=3319 in 1995) by age groups (total, under 75-year, and over 75-year populations) was linked to municipal SES indicators related to income, education, unemployment and living space, and two SES composite indices formulated by principle component analysis (Index 1 related to lower income and education, and Index 2 related to unemployment and overcrowding). The relation was assessed using mortality gradients by SES quintiles and Bayesian hierarchical Poisson regression. The results showed that a lower SES was related to higher mortality for all SES indicators and composite indices. The mortality gradient was steeper for the under 75-year population than the total and over 75-year populations, and the relation between mortality and income- and education-related indicators/index was stronger for males than for females. The time trend showed an increase in the relation for Index 2, while a decrease for Index 1. This study demonstrated that lower municipal SES had an adverse influence on population health, and the influence was marked for males and premature death. Although a substantial health disadvantage still remained in lower SES areas, the impact of SES factors on geographical health variation changed over time; the association with mortality has weakened for income and education, while it has strengthened for unemployment and living space.