The following limitations of the study should be considered. First, the way in which we formed our reference groups could be argued to be objective, thus not reflecting the groups people actually use for making social comparisons. Our data do not include any questions on people’s actual reference groups, rather we have based them on the assumption that people compare themselves to similar others – an argument that has also been used in other studies [5-8,13]. Based on previous studies, we would argue that our combinations of reference groups are sufficient for the present analyses.
Occupation was classified in accordance with the Swedish Socioeconomic Classification (SEI) and divided into the categories higher non-manual employees, lower non-manual employees, qualified manual workers, unqualified manual workers, self-employed and farmers. The total proportion of individuals who had an unclassifiable profession or had a missing value was 19%, somewhat higher among women than men. These individuals were excluded from the analyses. This is likely to have impacted the results when using occupation as a reference group and could be one reason why the analysis of top vs. bottom within the lowest quartile showed a lower HR in the crude model when using occupation as a reference group. In the excluded group of people, those with an unclassifiable profession or a missing value, the proportion of individuals with a low income is likely to be higher. However, we performed analyses using different reference groups and all showed a similar pattern, namely that relative income deprivation is significantly associated with mortality.
There are reasons to believe that income inequality has an impact on individual health outcomes, and different mechanisms and explanations within this relation have been discussed [2,23]. Social comparisons’, generating relative deprivation, has been put forward as one possible mechanism. There are different hypotheses as to the breeding ground for relative deprivation. It has been argued that a context that promotes values of egalitarianism may in turn promote feelings of relative deprivation, as it encourages people to make comparisons with affluent others . It could also be argued that psychosocial mechanisms may be more important in a setting where material deprivation, in an absolute sense, is not as common. However, even though these explanations seem important, this would not be as central for generating relative deprivation as large income disparities in a society.
In sum, our study suggests that relative deprivation, based on social comparisons of income, is significantly associated with premature mortality in Sweden, over and above the effect of absolute income. Relative deprivation was found to be most important among men, although weak among the poorest individuals.
The authors declare that they have no competing interests.
MÅY, NK, SH, IK all made substantial contributions to the manuscript. MÅY had the main responsibility for drafting the manuscript. NK and IK contributed substantially to the design of the study, revising the manuscript and interpretation of the results. SH performed the statistical analyses and contributed to the draft regarding methods and analyses. All authors read and approved the final version of the manuscript.
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Flow diagram over sample size.
We are grateful to Anthony Garcy and Susanna Toivanen for their input and suggestions regarding the data.
Funding: This work was supported by Stiftelsen Riksbankens Jubileumsfond, Sweden (to MÅY and SH) and (to NK) by the Health Labour Sciences Research Grant (Ministry of Health Labour and Welfare, Japan) and a Grant-in Aid for Scientific Research on Innovative Areas (No.22119504) (Ministry of Education, Culture, Sports, Science, and Technology, Japan).