Educational achievement and vocational career in twins - a Swedish national cohort study

To investigate how being born and raised as a twin is associated with IQ, educational achievement and vocational career.

Register study in a national birth cohort, complemented with a siblings study. The study population included 13,368 individuals born and raised as twins and 837,752 singletons, including 3019 siblings of twins, in the Swedish birth cohorts of 1973-1981. Our outcome measures were mean grade points on a five point scale from ninth grade of primary school at 15-16 years, IQ tests on a nine grade point scale from male conscripts at 18-19 years, highest completed education, disability benefits, work income and employment at 27-35 years of age.

Twins had slightly better mean grade point averages in ninth grade; +0.08 (95% CI 0.04-0.11) and more often had completed a university education in young adulthood; OR 1.16 (1.02-1.21) compared with singleton siblings, despite male twins having a slightly lower IQ at military conscription compared with male singletons. Employment rates, mean income and disability benefits were similar in twins and singletons.

Twins have slightly better educational careers and similar vocational careers compared with those born as singletons.