1 Department of Paediatric Respiratory and Sleep Medicine, Royal Hospital for Children and Young People, Edinburgh, EH16 4TJ, United Kingdom; Department of Child Life and Health, University of Edinburgh, United Kingdom. Electronic address: don.urquhart@nhslothian.scot.nhs.uk.
2 Paediatric Department, University Hospitals Würzburg, Germany.
3 School of Sport, Health and Exercise Science, Faculty of Science and Health, University of Portsmouth, United Kingdom.
4 Epidemiology, Biostatistics and Prevention Institute, University of Zurich, Switzerland.