1. Gastroenterology Division, Tufts Medical Center, Tufts University School of Medicine , Boston Massachusetts , USA
2. Center for Clinical Epidemiology, Odense University Hospital , Odense , Denmark
3. Research Unit of Clinical Epidemiology, Department of Clinical Research, University of Southern Denmark , Odense , Denmark
4. Center of Andrology and Fertility, Odense University Hospital , Odense , Denmark