PhD-research on how socioeconomic health inequalities develop

The mechanisms that underlie the development of socioeconomic inequalities in mental health and health behaviours in adolescence and young adulthood are not well understood. The main aim of Heiko Schmengler's dissertation is to gain more insight into the interplay of two processes that may contribute to the emergence of socioeconomic health inequalities: social causation and health-related selection.

Social causation emphasizes the role of the socioeconomic background of the family and of differences within the educational setting that underlie the development of health inequalities. Health-related selection refers to processes whereby health problems influence adolescents’ and young adults’ educational trajectories (direct health-related selection), or whereby individual differences already present in childhood (e.g., in cognitive skills, such as effortful control and IQ) predict later educational attainment as well as health characteristics or behaviours (indirect health-related selection). In addition, this dissertation examined whether associations between parental socioeconomic status (SES) and adolescent health behaviours differ between countries with low and high levels of social mobility. Country-level social mobility, like other social and cultural characteristics at the societal level, could influence the strength of the mechanisms that contribute to the development of health inequalities.

Schmengler's results highlight the importance of both social causation and health-related selection in the development of socioeconomic health inequalities in adolescence and young adulthood. Regarding inequalities in substance use, social causation processes appeared to be present. Early adolescents in the lower educational trajectories increased their drinking behaviour more strongly three years later. In young adulthood, the influence of the educational context was in the opposite direction, increasing the drinking behaviour of those in the higher educational trajectories. Possibly, this finding reflects the transition to college life amongst young adults following the higher educational tracks.

Conversely, following a lower educational trajectory was consistently associated with higher risks of smoking in adolescence and young adulthood, including after taking into account individual differences in effortful control, IQ, and genetics. Taken together, our findings suggest that educational inequalities in substance use are strongly influenced by differences in the social context across educational tracks, and that interventions aiming to address these disparities should bear in mind those differences. 

Regarding health-related selection, we found robust associations between ADHD symptoms and declines in educational level over the whole course of adolescence and young adulthood. This finding is consistent with earlier research showing that adolescents with mental health problems are at higher risk of having a lower SES in young adulthood. Providing additional support to these adolescents may be critical to both improve their educational outcomes and to decrease health inequalities. Lastly, higher levels of social mobility at the national level predicted larger inequalities by parental SES in physical activity, but not in any other health behaviours. This inconsistent result may hint at the complexity of the relationship between contextual-level social mobility and health inequalities.