Additional Information:
Funding text 1: All authors are part of the Family Justice Data Partnership (FJDP) - a collaboration between Lancaster University and Swansea University. The authors would like to thank other team members involved in the Family Justice Data Partnership including K Jones, A Akbari, A Lee, J Smart and S Thompson (Swansea University), and B Alrouh, S Doebler and J Harwin (Lancaster University). We would also like to thank the following for their support with this study: L Harker, Director, Nuffield Family Justice Observatory; Cafcass Cymru; Administrative Data Research Centre Wales; and Welsh government. The authors would like to acknowledge all the data providers who make data available for research, and the Adolescent Mental Health Data Platform for providing the substance use and mental health clinical codes used within this study. 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