Compositional and contextual approaches to the study of health behaviour and outcomes: using multi-level modelling to evaluate Wilkinson's income inequality hypothesis.

Much research into health behaviour and outcomes involves evaluating compositional and contextual hypotheses: the former suggest that behaviour/outcomes are a function of the individual's characteristics alone, whereas the latter argue for the importance of contextual/environmental influences. Wilkinson has presented a contextual argument relating inter-country variations in mortality rates to income inequalities; Gravelle has countered this arguing that Wilkinson's findings are a statistical artefact and that a compositional approach, relating mortality to individual income, is sufficient. Discriminating between these two cases requires a methodology combining the two approaches. Multi-level modelling is proposed and applied to two data sets. The results sustain Gravelle's case, emphasising the role of compositional rather than contextual variables in accounting for inter-country variations in health status.