Schooling has Smaller or Insignificant Effects on Adult Health in the US than Suggested by Cross-Sectional Associations: New Estimates Using Relatively Large Samples of Identical Twins

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Adult health outcomes and health behaviors generally are strongly associated with schooling attainment. But such associations do not necessarily imply that schooling has causal effects on health outcomes and behaviors of the magnitudes of the associations. Schooling may be proxying for unobserved factors that are related to genetics and family background. Recently several studies have used within-identical (monozygotic, MZ) twins methods to control for those unobserved factors that are shared completely by identical twins. Estimates based on relatively small samples for the US, as well as some larger samples for other countries, suggest that causal impacts of schooling on health outcomes and behaviors are insignificant or much smaller than suggested by cross-sectional associations. This study contributes new estimates of cross-sectional associations and within-MZ causal effects of twins using three relatively large US samples: Mid-Atlantic Twin Registry, Minnesota Twin Registry and NAS-NRC Twin Registry of WWII Military Veterans. The estimates suggest that schooling is significantly associated with numerous health outcomes and behaviors in the US. However if within-MZ twins estimators are used to control for unobserved factors, there is no causal relationship between schooling and better health behaviors. There is some evidence that more schooling causally affects self-reported health and overweight status, net of unobservable cofounders, though not to the extent that cross-sectional associations suggest. Finally, spousal schooling is associated with better health outcomes and behaviors, but there is no evidence of any causal effect.