At age 17, the twins reported on their current student status. Responses were classified into an ordinal variable with three categories: (0) Not studying currently, (1) In vocational training, (2) In high-school. In young adulthood, educational attainment was based on a questionnaire item on the highest level of completed education, ranging from compulsory schooling to tertiary education. In addition, for those twins who had not yet completed their education, ongoing studies were treated as the final, expected education. Educational attainment in young adulthood was coded into four ordered categories: (0) Compulsory education only, (1) Vocational secondary education, (2) Academic secondary education, and (3) Tertiary education.
