1. Unit of Preventive Gastroenterology, Department of Paediatrics, Università di Firenze, 50132 Florence, Italy
2. Department of General Practice and Primary Health Care, University of Auckland, Auckland, New Zealand
3. Department of Physiology and Pharmacology, Robert F. Furchgott Center for Neural and Behavioral Sciences, State University of New York Downstate Medical Center, Brooklyn, NY, USA
4. AMC, 1100 DD Amsterdam, The Netherlands
5. Department of Statistics, Università di Firenze, Florence, Italy
6. Paediatric Unit, Università di Verona, Verona, Italy