The association between rates of self-harm and demographic data was assessed using χ2 statistical tests and univariable logistic regression models. As information on self-harm was not available for the whole ALSPAC cohort (due to those who were lost to follow up, and those who received the questionnaire but did not return it) there was the potential for bias both in the estimated prevalence and also in the association with demographic factors. This was explored using a multiple imputation, more details of which can be found in the section below. A secondary analysis looked in more detail at the reported cases of self-harm. The proportion of respondents who fell into each category for frequency of self-harm, reasons for it, and consequences in terms of subsequent feelings and the need to seek medical help were tabulated overall, and comparisons were made by gender using χ2 statistical tests. The characteristics of those who self-harmed with desire to die and those who self-harmed without desire to die the most recent time were compared using χ2 statistical tests. Finally, prevalence of suicidal thoughts and plans
