1. Research Unit for General Practice, Aarhus C, Denmark
2. Department of Public Health, Aarhus University, Aarhus C, Denmark
3. Department of Haematology, Odense University Hospital, Odense C, Denmark
4. Department of Clinical Epidemiology, Aarhus University Hospital, Palle Juul-Jensens, Aarhus N, Denmark
5. Department of Clinical Biochemistry, Aalborg University Hospital, Aalborg, Denmark