The effects of poverty on health in early childhood have been recognised for many years and have generated a prolonged and often acrimonious causal debate.¹ Explanations have broadly fallen into two groups: those that focus on characteristics of the poor themselves such as the inferiority of their “genetic stock”, their poor hygiene, their poor childcare practices, or their health related behaviours such as smoking and those that focus on the effects of poverty itself and the societal structures that generate it.

Given the longstanding interest in poverty and child health, it is surprising that, as Séguin et al² state in their paper in this issue of the journal, the aspects of socioeconomic status that are important to children’s health remain unclear. Part of the explanation for this continuing lack of clarity lies in the tendency to treat different components of socioeconomic status …