1. Queen Mary University of London; Centre for Child Health, Blizard Institute; London UK E1 2AT
2. University College London; EPPI-Centre, Social Science Research Unit, UCL Institute of Education; 20 Bedford Way London UK WC1H 0AL
3. Cochrane Central Executive; Editorial & Methods Department; St Albans House 57-59 Haymarket London UK SW1Y 4QX
4. The University of Newcastle; School of Nursing and Midwifery, Priority Reseach Centre for Asthma and Respiratory Disease; Locked Bag 1000 New Lambtion Newcastle NSW Australia 2305