JK co-conceived and designed the study, developed the self-harm questions, conducted the main data analysis and wrote the paper. JH advised on the ALSPAC dataset, contributed to the statistical analysis, conducted the missing data analysis, and co-wrote the methods and results sections. GL contributed to the study design, the self-harm questions and the data analysis and interpretation, and critically revised the manuscript. JE contributed to the data analysis and interpretation, and critically revised the manuscript. DG co-conceived and designed the study and self-harm questions, advised on data analysis, and contributed to the interpretation of findings and the writing of the paper. All authors read and approved the final manuscript.
