1. Department of Surgery, Södersjukhuset, Stockholm, Sweden
2. Department of Surgery, Akademiska Sjukhuset, Uppsala, Sweden
3. Department of Surgery, Mora District Hospital, Mora, Sweden
4. Department of Surgery, Östersund Hospital, Östersund, Sweden
5. Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden
6. Department of Surgery, University Hospital of Lund, Lund, Sweden