Can Additional Years of Schooling Reduce Social Differences in Mental Health Related to Genetic Predisposition?

Dobewall, Henrik

The study uses the Finnish compulsory school reform of the 70s as a natural experiment and examines its effect on mental illness relying on novel molecular genetic instruments, namely polygenic scores (PGS). The reform was essential for defining the egalitarian welfare state Finland as it allowed for the educational expansion in terms of 3 years longer comprehensive schooling and better access to upper-secondary degrees and higher education institutions for later born generations. We build on a causal inference framework (differences in differences design) and follow-up on previous studies from UK and Sweden.

Research questions:

Do additional years of schooling reduce the association between genetic predisposition and mental illness (gene-environment GxE interaction)?
Do some social groups, defined by gender and parental socioeconomic status, benefit more / less from the educational reform than others (heterogeneous effects)?

Genetically-informed register data -cohorts born between 1958 and 1970- was split into those affected by the Finnish compulsory school reform and those who went to school before the change in obligatory years of schooling took place. Minimum years of schooling were measured as exogenous variable, as cohorts were affected differently by the school reform dependent on region of residency. Genetic propensity for mental illness was measured with PGSs. Mental illness diagnoses based on ICD-10 classification recorded in public specialized health care and reimbursement for prescribed medication were used as outcomes.

We did not find robust evidence that the studied educational reform reduced the effect of genetic predisposition on being diagnosed with a mental illness or medication use. Identifying GxE interactions is challenging due to lack of statistical power. A few signals for heterogeneous effects were observed, but no association would survive correction for multiple testing. Policy implications will be discussed.