Demographic data, collected in previous ALSPAC questionnaires, were included in the analysis, to enable comparison of responders and non-responders, and to identify key psychosocial characteristics associated with self-harm. The following variables were used: i) mother’s social class (manual/intermediate/non-manual), ii) mother’s highest educational level (A level or ‘advanced level’ which are post compulsory schooling qualifications or higher education degree/O level or ‘ordinary level’ which are now defunct examinations taken at the end of compulsory schooling by students deemed more academically able/lower than O level which includes any other qualifications of a lower academic standard or no qualifications at all) as reported when the participant was first born, iii) mother’s score on the Edinburgh Postnatal Depression Scale (EPDS) (which has been validated for use in non-postnatal women [21], and was introduced in ALSPAC during pregnancy then retained for consistency) - using the cut-off point of 12/13 recommended for identifying a depressive illness [22] - when the participant was 11 years old, iv) participant’s gender, v) participant’s ethnicity (white/non-white) as reported by the mother prior to birth, vi) participant’s performance in national examinations
