Associations between relative income and mortality in Norway: a register-based study.

BACKGROUND: Current research on health inequalities suggests that not only an individual's absolute level of income but also his/her relative position in the income hierarchy could have health consequences. This study examines whether relative income was associated with individuals' mortality in Norway during the 1990s.

METHODS: Data were formed by linkages of Norwegian administrative registers. This study analyses 1.68 million men and women (age group: 30-66 years) with disposable income (1993) in the range 60,000-210,000 Norwegian Kroner. Relative income was calculated as deviations in per cent from the median income in the surrounding residential area. The outcome variable was deaths in 1994-1999. Effects of relative income on mortality were estimated by multiple logistic regression analyses, separately in 13 narrow brackets of absolute income. Adjustments were made for sex, education, marital status, and other individual-level mortality predictors.

RESULTS: Low relative income compared with the median in residential regions with populations above 20,000 inhabitants was associated with higher mortality among those with medium and lower absolute income. The excess risk increased progressively the lower the level of absolute income. Among those with higher absolute income, however, relative income was not associated with mortality. Moreover, when relative income was considered in relation to the median in small municipalities, almost no effect on mortality was observed.

CONCLUSION: In Norway during the 1990s, having low relative income constituted an additional mortality risk among individuals with middle or lower absolute incomes and when relative income was calculated in relation to the average in medium-sized or larger regions.