Educational attainment or achievement was assessed through the general certificate of secondary education (GCSE) and advanced level (A level) qualifications. GCSEs are qualifications usually obtained at the end of compulsory schooling in Great Britain, at age 16 years, and are graded from A*-G. A levels are typically taken at age 18 years, after compulsory school examinations. A minimum of three A levels is usually required for university entrance. In the United States these qualifications are loosely comparable to a general high school achievement test (GCSE) and a college entrance examination, such as the scholastic achievement test (A level). We obtained GCSE results from the national pupil database key stage 4 dataset, recording pupil census and assessment data for all pupils in English government maintained schools.21 We dichotomised participants according to whether they obtained five or more GCSE (or equivalent) qualifications at grades A*-C; a nationally recognised threshold of attainment. Since we assessed the lifetime history of self harm at age 16 years and the age of onset was not known, it is possible that GCSE examinations may have preceded or occurred concurrently with self harm at baseline for some participants.
