title: Change in income and change in self-rated health: Systematic review of studies using repeated measures to control for confounding bias.
abstract: It is generally assumed that income is strongly and positively associated with health. However, much of the evidence supporting this assumption comes from cross-sectional data or analyses that have not fully accounted for biases from confounding and health selection (the reverse pathway from health to income). This paper reports results of a systematic review of panel and longitudinal studies investigating whether changes in income led to changes in self-rated health (SRH) in adults. A variety of electronic databases were searched, up until January 2010, and thirteen studies were included, using data from five different panel or longitudinal studies. The majority of studies found a small, positive and statistically significant association of income with SRH, which was much reduced after controlling for unmeasured confounders and/or health selection. Residual bias, particularly from measurement error, probably reduced this association to the null. Most studies investigated short-term associations between income and SRH or the effect of temporary (usually one year) income changes or shocks, so did not rule out possibly stronger associations between health and longer-term average income or income lagged over longer time periods. Nevertheless, the true causal short-term relationship between income and health, estimated by longitudinal studies of income change and SRH that control for confounding, may be much smaller than that suggested by previous, mostly cross-sectional, research.
authors.affiliation: Department of Public Health, University of Otago, Wellington School of Medicine and Health Sciences, 3 Mein St, Newtown, Wellington, New Zealand. fiona.imlach-gunasekara@otago.ac.nz
authors.forename: Fiona Imlach
authors.initials: FI
authors.lastname: Gunasekara
authors.forename: Kristie
authors.initials: K
authors.lastname: Carter
authors.forename: Tony
authors.initials: T
authors.lastname: Blakely
mesh_terms: D015982:Bias; D015986:Confounding Factors, Epidemiologic; D059026:Diagnostic Self Evaluation; D006304:Health Status; D006801:Humans; D007182:Income; D008137:Longitudinal Studies; D012107:Research Design