Can we disentangle life course processes of accumulation, critical period and social mobility? An analysis of disadvantaged socio-economic positions and myocardial infarction in the Stockholm Heart Epidemiology Program.

The accumulation hypothesis would propose that the longer the duration of exposure to disadvantaged socio-economic position, the greater the risk of myocardial infarction. However there may be a danger of confounding between accumulation and possibly more complex combinations of critical periods of exposure and social mobility. The objective of this paper is to investigate the possibility of distinguishing between these alternatives. We used a population based case-control study (Stockholm Heart Epidemiology Programme) of all incident first events of myocardial infarction among men and women, living in the Stockholm region 1992-94. The analyses were restricted to men 53-70 years, 511 cases and 716 controls. From a full occupational history each subject was categorized as manual worker or non-manual at three stages of the life course, childhood (from parent's occupation), at the ages 25-29 and 51-55, resulting in 8 possible socio-economic trajectories. We found a graded response to the accumulation of disadvantaged socio-economic positions over the life course. However, we also found evidence for effects of critical periods and of social mobility. A conceptual analysis showed that there are, for theoretical reasons, only a limited number of trajectories available, too small to form distinct empirical categories of each hypothesis. The empirical task of disentangling the life course hypotheses of critical period, social mobility and accumulation is therefore comparable to the problem of separating age, period, and cohort effects. Accordingly, the interpretation must depend on prior knowledge of more specific causal mechanisms.