Use of the Yitzhaki Index as a test of relative deprivation for health outcomes: a review of recent literature.

We reviewed the empirical studies published between 2000 and 2010 that test the relative deprivation (RD) hypothesis in relation to population health. Our review focuses primarily on 14 studies using the Yitzhaki Index and related relative income measures. We summarize their main findings by health outcome, address methodological challenges in measuring RD, and identify several gaps in the literature as well as future directions for research in this area. Gaps in the evidence include the need for longitudinal studies with stronger causal designs - for example, examining changes in RD in relation to changes in health outcomes, with careful control for confounding by individual income and other indicators of socioeconomic position. Defining the appropriate reference group (from which people make social comparisons) poses a major empirical challenge, as evidenced by the fact that the measurement of RD has not materially advanced since Yitzhaki's original formulation in 1979. More innovative approaches to operationalizing RD are needed - including the measurement of RD in dimensions other than income, incorporating inter-generational comparisons; and attempting exogenous manipulation of RD, e.g. through laboratory-based experiments.