rustration and injustice. Researchers taking this approach have sought to demonstrate that, over and above the increased command over resources, income matters to individuals because it is the basis of social comparisons between a person and his/her reference group [5-8]. Social comparisons have previously been analyzed as a possible mechanism underlying the income-health relation [7-9], and have been linked with happiness  as well as outcomes such as deviant behaviour among adolescents .
Drawing on Runciman’s theory, Yitzhaki  proposed an index for estimating relative deprivation, calculating the accumulated shortfall between one’s own income and the incomes of all others in one’s reference group. Recent studies have used the Yitzhaki index when analyzing the importance of individual relative deprivation for health [5,6,13-17]. Studies in the US have generally reported evidence in support of the hypothesis that relative deprivation is associated with increased risks of mortality , mental health services utilization , and poor self-rated health . In Japan, Kondo and colleagues studied the association between relative deprivation, measured by the Yitzhaki index, and self-rated health . The overall result indicated that relative deprivation was associated with poor self-rated health, regardless of the reference group used and independent of absolute income. By contrast, studies based in the UK have failed to demonstrate an association between relative deprivation and health [16,17].
The goal of the present study was to conduct an empirical test of relative deprivation and mortality in Sweden – a society that is characterized by a strong egalitarian ethos, as well as a relatively flat degree of income dispersion (in contrast to countries such as the US or UK) . According to Bernburg , the individual experience of relative deprivation may be more prominent in a context that promotes values such as egalitarianism, upward social mobility, equal opportunity and individual achievement. In the present study, we therefore sought to analyze the importance of individual-level relative deprivation, as measured by the Yitzhaki index, for all-cause mortality in the Swedish population.
We used prospective longitudinal data from the Swedish population with baseline collection in 1990 and mortality follow-up until 2006. The Swedish Work and Mortality Data Base, maintained at the Centre for Health Equity Studies, was created to study how work, income and labour market position combine to impact morbidity and mortality. The data were based on a linkage of the National Population and Housing Censuses, the Total Population Register (RTB), the Longitudinal Data Base on Education, Income and Employment (LOUISE), the Cause of Death Register and inpatient registers. When restricting the data to individuals alive January 1 1990 and aged 25–64years, the data included a total of 4.7 million individuals, for whom we conducted a mortality follow-up until 2006 [see Additional file 1 for sample size]. From this cohort, we excluded all individuals who lacked income data, all individuals who had emigrated and for whom we do not have any death data (N=4 227 490). The occupation variable derives from the 1990 National Population and Housing Census, and 19% had either unclassifiable occupations or missing values, for example persons on sick leave, students or unemployed. These 19% were excluded when using occupation in the models. Ethical permission (no 02–481) was provided by the Regional Ethics Committee at Karolinska Institute in Stockholm.
The central exposure variable, the measure of relative deprivation was calculated using the Yitzhaki index , in a similar way as done in previous studies [5,13,15]. The index calculates the relative deprivation for each individual by summarizing the differences in income between that individual and all individuals with a higher income in that person’s reference group, taking the size of the reference group into consideration. Relative deprivation for the individual i is the sum of the income gap between i and j (yj – y