s and occupation, the HR of the top vs. bottom quartile among men is attenuated to the values ranging between 1.693 and 1.821, but still statistically significant. Among women, these results vary between 1.127 (95%CI: 1.097-1.157) and 1.182 (95%CI: 1.151-1.213). In Model 3, we also adjust for absolute income. Although this additional adjustment attenuates the association between relative deprivation and mortality, the HRs remain statistically significant among men (HRs were between 1.668 and 1.751), whereas the HRs among women largely attenuate to lower values (between 0.992 and 1.155).
To further disentangle the relationship between relative deprivation and income, we calculated HRs for mortality by level of relative deprivation within income quartiles (Table (Table3).3). In males, this clearly illustrates the differences in HR depending on income level where individuals in the lowest quartile are not affected by relative deprivation. The multicolinearity between relative deprivation and income was tested by calculating the correlation coefficient and revealed a moderate overall association (r=− 0.45 Y index age groups; r=−0.45 Y index living region; r=−0.50 Y index occupation).
The overall finding is that the effect is larger in the reference groups defined by living region and by age group, and larger among men. Among men, there is no effect of relative deprivation on mortality within the lowest income quartile (Q1) regardless of the reference group used. However, there seems to be a threshold to the second lowest quartile (Q2) where the effect significantly differs from the lowest (Q1). Among women, only when defining reference group by living region there is a significant, although very small, effect.
Based on longitudinal data from the Swedish population with a mortality follow-up over a 16-year period, including a total of 4.7 million individuals aged 25–64years, the present study makes a unique contribution to explaining the hypothesized mechanism of relative deprivation in the income-health relation. The primary findings of the present study are that relative income deprivation was significantly associated with premature mortality, irrespective of sociodemographic status, including individual income, and that this association was stronger among men than women. The effect of relative deprivation on mortality was weak among the poorest.
When analyzing relative deprivation as was done here, we do not know which reference groups are the most important. People tend to make a vast number of comparisons, but not all are important to feelings of relative deprivation and not all are important to health. In the present study, we used different types of objectively defined reference groups, all based on the idea that people compare themselves with similar others: same age group, same occupational group, same living region or a combination of these. Our results show an effect of relative deprivation on mortality for most of the tested reference groups, also after adjustments were made. These results resemble findings from previous studies showing relative deprivation to be important, although of different degree, irrespective of how reference groups were formed [5-8,13]. The Yitzhaki index is a measure of individual-level relative deprivation, albeit linked to income inequality as it is expected to increase with increasing disparities. Previous studies on the relation between income inequalities and health show mixed results, where the most consistent findings was reported in the United States when income distribution was measured at the state level . However, analysing the importance of income inequality in Sweden, a previous study by Gerdtham and Johannesson did not find support for the relation to mortality . Even though relative deprivation is linked to income inequality, the measure of relative deprivation captures individual level psychosocial impacts to a larger extent than for example the Gini index.
In line with previous results, we find that the effect of relative deprivation is more important for men than for wom