Self harm in the past year was assessed through self report questionnaire sent to participants at age 21 years: mean age 20 years 11 months (SD 6 months). We assessed the lifetime history of self harm with the same item used in the previous questionnaire assessment at age 16 years “have you ever hurt yourself on purpose in any way (for example, by taking an overdose of pills or by cutting yourself)?” Participants who responded positively were then asked a further question about when they last harmed themselves (response options: In the last week/more than a week ago, but in the last year/more than a year ago). We dichotomised this response to create a binary indicator of self harm in the past year. Participants were not asked about suicidal intent during the past year. Sixty five per cent of those with information on self harm with and without suicidal intent at age 16 years returned the questionnaire at age 21 years (n=3128/4799).
