School performance and the social gradient in young adult death in Norway.

Young adults from low socioeconomic backgrounds face an increased risk of early mortality. Here we utilize population-wide data from 17 Norwegian birth cohorts (N = 986,573) to assess whether this risk gradient was explained by early-life educational performance, specifically grade point average at 16 years of age. We show that the gradients in both parental education and income largely disappeared when adjusting for school performance in the models. Specifically, among boys, those with the lowest parental education had an unadjusted hazard ratio (HR) of 2.04 (95% confidence interval (CI) 1.86-2.22) compared with peers with the highest parental education, while for girls, the HR was 1.64 (95% CI 1.35-1.93). After adjusting for school performance, these estimates dropped to 0.99 (95% CI 0.79-1.19) for boys and 0.87 (95% CI 0.55-1.19) for girls. Similarly, the mortality risk for those from the lowest parental income quartile decreased from 1.79 (95% CI 1.67-1.91) to 1.25 (95% CI 1.12-1.38) for boys and from 1.63 (95% CI 1.44-1.83) to 1.24 (95% CI 1.03-1.46) for girls. Low educational performance remained strongly associated with early mortality in analyses accounting for unobserved heterogeneity at the family level; boys with a grade point average in the lowest quartile had an HR of 3.04 (95% CI 2.38-3.89), while for girls, the HR was 1.79 (95% CI 1.22-2.63). External causes of death, particularly accidents and poisoning, were most overrepresented among individuals with poor school performance.