1. Clinical Operational Research Unit, Department of Mathematics (Q.H., E.H., C.P., S.C., F.E.-P.
2. Population, Policy and Practice Programme, Great Ormond Street Institute of Child Health (D.R.), University College London.
3. Institute of Cardiovascular Science (V.T., K.L.B.), University College London.
4. Great Ormond Street Hospital Biomedical Research Centre, London (V.T., K.L,B,).
5. Paediatric Cardiology and Cardiac Surgery, Birmingham Children’s Hospital, Birmingham (N.E.D., T.J.J., A.N.S., C.M.).
6. Institute of Cardiovascular Sciences, University of Birmingham (N.E.D., T.J.J., A.N.S.).
7. Paediatric Cardiology, Evelina London Children’s Hospital (H.B.-R.).
8. Paediatric Cardiology, Royal Brompton and Harefield NHS Foundation Trust, London (R.C.G.F.).