[Skewed income distribution and geographical mortality differences].

BACKGROUND: A prominent theme in current health research is whether large income inequality in a society in itself has negative consequences for population health, in addition to the effects of individual risk factors. The present study investigates whether mortality in Norway during the 1990s was higher in geographical regions with particularly skewed income distributions.

MATERIAL AND METHODS: Register data for all inhabitants aged 25-66 in Norway in 1992 were used (N = approx. 2.2 millions), including information about deaths 1993-99. Norwegian municipalities were grouped into 23 regions. Gini coefficients indicating the degree of inequality in the income distribution were calculated for each region. Deaths 1993-99 were analysed by means of multiple logistic regression.

RESULTS: Odds ratios for deaths 1993-99 were strongly influenced by well-known individual risk factors such as sex, age, marital status, educational level, personal income, and disability. In addition, odds ratios for death were significantly associated with the regions' gini coefficients when adjustments were made for average income level in the regions. This effect of income inequality was pronounced for people with low education, but almost absent among those with higher education. Moreover, the income inequality effect was to some extent driven by special circumstances in Oslo, Norway's capital city, with its high mortality among the less educated and a particularly non-egalitarian income distribution. However, the pattern of higher mortality associated with higher levels of income inequality among the less educated was also observed in the 22 regions outside Oslo.

INTERPRETATION: We found a discernible, although not very strong, association between regional income inequality and mortality levels among the less educated. Several interpretations for this statistical tendency could be proposed; the social processes generating this tendency should be clarified further.