1. From the Laboratorio di Epidemiologia e Biostatistica, Istituto di Ricovero e Cura a Carattere Scientifico S De Bellis, Ospedale Specializzato in Gastroenterologia, Castellana, Bari, Italy, and the Department of Social and Preventive Medicine, State University of New York at Buffalo, School of Medicine and Biomedical Sciences, Buffalo.