1. Department of Neuroscience, NTNU Norwegian University of Science and Technology, Trondheim, Norway;
2. Department of Health and Rehabilitation/Physiotherapy, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden;
3. Duke Evidence Synthesis Group, Duke Clinical Research Institute, Durham, North Carolina;
4. Department of Medicine, Duke University School of Medicine, Durham, North Carolina;
5. Center for Health Services Research in Primary Care, Durham Veterans Affairs Medical Center, Durham, North Carolina;
6. Section for Medicine, NTNU University Library, NTNU Norwegian University of Science and Technology, Trondheim, Norway; and
7. Norwegian Advisory Unit on Headaches, St Olavs Hospital, Trondheim, Norway