Children were interviewed about their relationships with their parents, and then the researchers looked at how much cost each child in the study had generated in terms of public services – whether that was special meetings at school due to being upset, or social services, or even involvement with the criminal justice system. Researchers controlled for antisocial behaviour, gender, social class and income, and even after all that, found that a child not having a secure attachment to their parents accounted for a significant difference in cost.