Household income and health problems during a period of labour-market change and widening income inequalities - A study among the Finnish population between 1987 and 2007

Income inequalities widened considerably from 1987 to 2007 in Finland. We compared the association between household income and health problems across three periods and in several different ways of modelling the dependence. Our aim was to find out whether the change in the distribution of income might have led to wider income-related inequalities in health problems. The data represent an 11-per-cent random sample of the Finnish population, and we restricted the analysed sample to those between 18 and 67 years of age and not in receipt of any pension in each of the three six-year periods examined (n between 280,106 and 291,198). The health outcome was sickness-allowance days compensated. Household-equivalent taxable income was applied with two different scale transformations: firstly, as real income adjusted for price level and secondly, as rank position on the income distribution. We used negative binomial regression models, with and without zero inflation, as well as decomposition analysis. We found that sickness-allowance days decreased with increasing income, while differences in the shape and magnitude of the association were found between the scales and the periods. During the study period the association strengthened considerably at both the lowest fifth and the top fifth of the rank scale, while the observed per-unit effect of real income changed less. Decomposition analysis suggested that slightly less than half of the observed increase in concentration of health problems at lower end of the rank scale could be accounted for by the change in real income distribution. The results indicate that widening differences in household consumption potential may have contributed to an intensified impact of household income on inequalities in health problems. Explaining the change only in terms of consumption potential, however, was problematic, and changes in the interdependence of labour-market advantage and health problems are likely to contribute as well.