 The choice of the social variable in terms of which to describe some social gradient in health can be made on a number of different grounds. One obvious ground would be to choose the variable(s) that came closest to conveying the operative causal mechanism(s). Another ground would be to choose the variable(s) that have independent moral and/or political significance, such as race and gender. These grounds need not exclude each other and there may be a case for choosing the same variable on both grounds. The second ground acquires a special relevance if health inequalities suffered by individuals who also suffer, for example, from racial discrimination are more unjust than health inequalities (of the same magnitude) suffered in the absence of racial discrimination. If one injustice can compound another, then the choice of social variable may affect the kind of inequality in health at issue, and not simply its magnitude.