Commentary: Selected samples and nebulous measures: some methodological difficulties in life-course epidemiology

Ramsay et al.’s article contributes to a growing body of research on early life characteristics that predict health in adulthood. This research demonstrates that adults who lived in deprived socio-economic circumstances as children aremore likely to suffer from cardiovascular disease than adults who had privileged childhoods; an association that holds even among people with comparable indicators of adult socio-economic position (SEP). These articles provide a welcome impetus to consider how adult health is shaped by early life experiences, but they face a number of methodological problems that compromise causal inference regarding the effects of childhood social conditions on adult health. In this commentary, I wish to focus on just two of these problems: loss to follow-up and inadequate measurement. Throughout, I assume that the primary causal question of interest is how adult health would differ if we intervened to change childhood SEP, and a secondary causal question is how adult health would differ if we intervened to change not only childhood SEP but also adult SEP or adult behavioural risk factors. My goal in highlighting these difficulties is to prompt life-course researchers to present evidence addressing these possible biases, and improve our ability to interpret the now well-established association between early childhood circumstances and adult health.