Of the 9384 participants that received the questionnaire, 4855 returned it (51.7%) and 4810 (51.3%) responded to the self-harm questions. The mean age of respondents at the time the questionnaire was completed was 16 years and 8 months (standard deviation (SD) 2.9 months). Those who returned the questionnaire were more likely than non-respondents to be female, have a mother in a non-manual social class, and to have relatively high educational qualifications (see Table 1 for more details).
