Inequalities in self-rated health in Japan 1986-2007 according to household income and a novel occupational classification: national sampling survey series

Background Japan, for the past two decades, has seen economic stagnation and substantial social change. We examined whether health inequalities increased over this period. Methods Using eight triennial waves of a series of large nationally representative surveys between 1986 and 2007 (n=398303), temporal trends in relative and slope indices of inequality (RII, SII, respectively) were tested based on self-rated health in relation to theory-based social class and household income. Results Age-standardised prevalence of self-rated fair or poor health showed V-shaped time trends in both sexes with the lowest prevalence in early/mid-1990s. In 1986, RII and SII in household social class and income were significant for both sexes. In men, RII and SII according to income showed significant narrowing of temporal trends in poor health (-1.4% and -0.1% annually, respectively), but these were stable in women. After multilevel multiple imputation for missing income data, the findings in men were not altered but narrowing trends became evident and significant in women (-1% and -0.1% annually, respectively). Inequality indices for social class remained constant over the study period in both sexes. Conclusions Relative and absolute health inequalities for social class and income based on self-rated fair or poor health narrowed or remained stable between 1986 and 2007, despite the economic stagnation and adverse social changes. Overall population health across socioeconomic groups initially improved but then worsened. The positive finding regarding the health inequality trend seen in the Japanese context is informative for the wider international community during this period of economic uncertainty.