1. Pediatric Pulmonology Unit, First Department of Pediatrics; University of Athens School of Medicine and Aghia Sophia Children's Hospital; Athens Greece
2. Center for Clinical Evidence Synthesis, The Institute for Clinical Research and Health Policy Studies; Tufts Medical Center, Tufts University School of Medicine; Boston Massachusetts
3. Department of Biomathematics; University of Thessaly School of Medicine; Larissa Greece