Birth order: self-injurious and suicidal behaviour among adolescents.

A sample of 2553 children and adolescents in a psychiatry clinic in Germany were assessed using a structured interview inventory that included history of self-injurious behaviour, suicidal intent and socially disruptive and threatening behaviour, and diverse socio-demographic variables (the basis documentation or 'Ba-Do'). Birth order was associated with both suicidal and self-injurious behaviour, middle children being most likely to exhibit such behaviour. Females were more than twice as likely to have self-injured than males. Comparisons of birth order groups within gender found no significant differences in suicidal behaviour between birth positions for males, however among females, middle children were much more likely to have attempted suicide. Conversely, there was no difference in self-injurious behaviour among birth positions in females, but among males, middle children were significantly more likely to have self-injured than firstborns, only children or lastborns. The number of siblings in the family was significantly correlated with both suicidal history (r = 0.12, p < 0.001) and self-injurious behaviour (r = 0.10, p < 0.001). The risk of suicidal behaviour was highest for those with four or more siblings.