The axes of social differentiation and the evidence base on health equity

The term health gradient is widely used to describe the ways in which mortality and morbidity are related to social position; the higher the social status the better the health, and conversely, the lower the social status the worse the health. This population level pattern has been noted since modern records began.1 This paper considers some of the theoretical, conceptual and methodological issues which are attached to the health gradient and the implications of these for the methods of evidence accumulation and synthesis and evidence-based medicine more generally.