1. Research Unit for General Practice in the North Denmark Region, Nord-KAP, Aalborg, Denmark.
2. Institute of Public Health, Aarhus University, Aarhus, Denmark.
3. Surgical Research Unit, Department of Surgery, Herning Regional Hospital, Herning, Denmark.
4. Research Unit for General Practice, Aarhus University, Aarhus, Denmark.
5. Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus C, Denmark.
6. Department of Clinical Pharmacology, Bispebjerg Hospital and Laboratory of Clinical Pharmacology Q, Copenhagen, Denmark.
7. Clinical Institute, University Hospital of Aarhus, Aarhus C, Denmark.
8. Surgical Research Unit, Department of Surgery P, University Hospital of Aarhus, Aarhus C, Denmark.