el 2 we adjusted for age group, marital status and occupation, and in Model 3 we also added income.
The descriptive analyses in Table Table11 show the number of deceased by age group, marital status and occupational group. The number of deceased is higher among males than females. The proportion of deceased during the follow-up also varies across marital status and occupation, with higher rates among divorced, widows/widowers and unqualified manual workers. Descriptive analyses also show the median relative deprivation within reference groups used. For an individual, having a lower value on the relative income deprivation index means having a higher income within the reference group. Having a value of 0, means having the highest income within the specific reference group. The median relative income deprivation differs depending on whether living region, age group or occupation has been used. The lowest value was found when combining these three, since the income diversity is smaller when reference groups become more specific.
In order to illustrate the possibility of non-linearity in the association between relative deprivation and mortality, we calculated HR for continuous as well as quartiled relative deprivation (Table (Table2).2). Cox regression showed that, among men, relative deprivation was significantly associated with mortality regardless of the definition of reference groups for which we calculated relative deprivation. The crude HRs for mortality by 10 000 SEK unit increase in relative deprivation are between 1.069 (95% confidence intervals [CI]: 1.066 -1.072) and 1.109 (95%CI: 1.107-1.111), depending on the reference group. The crude HRs for women range between 0.986 (0.982-0.990) and 1.118 (1.116 – 1.120). The crude HR of the highest versus the lowest quartile is between 1.414 (95%CI: 1.392-1.437) and 2.503 (95%CI: 2.474-2.532) among men, and between 0.958 (95%CI: 0.937 - 0.980) and 2.082 (95%CI: 2.041 - 2.123) among women, depending on the reference group used. Adjusting for age group, marital status 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