1. University Medical Center Groningen; Beatrix Children's Hospital and Department of Epidemiology; PO Box 30.001 (CA80) 9700RB Groningen Netherlands
2. The University of Sydney; Department of Paediatrics and Child Health; Locked Bag 4001 Westmead Australia NSW 2145
3. University Medical Center Utrecht; Julius Center for Health Sciences and Primary Care; P.O.Box 85500 Utrecht Netherlands 3508 AB
4. Durham University Queen's Campus; School of Medicine, Pharmacy and Health; Durham UK TS17 6BH
5. University Medical Center Groningen; Department of Epidemiology; Groningen Netherlands
6. Durham University; Department of Sport and Exercise Science; 42 Old Elvet Durham UK DH13HN