1. Danish Headache Center, Rigshospitalet-Glostrup, University of Copenhagen , Glostrup , Denmark
2. Danish Knowledge Center on Headache Disorders, Rigshospitalet-Glostrup , Glostrup , Denmark
3. GP Cluster in Vejle , Vejle , Denmark
4. Research Unit for General Practice, Department of Public Health, University of Southern Denmark, Odense , Denmark
5. Department of General Practice, Institute of Health and Society, University of Oslo , Oslo , Norway