1. BIDMC Comprehensive Headache Center , Department of Neurology and Department of Anesthesia, Critical Care and Pain Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center , Boston , MA , USA
2. Department of Clinical Medicine , Faculty of Health Sciences , University of Copenhagen , Copenhagen , Denmark
3. Department of Neurology , Albert Einstein College of Medicine , Bronx , NY , USA
4. Department of Public Health, Section of Social Medicine , University of Copenhagen , Copenhagen , Denmark
5. QualityMetric , LLC , Johnston , RI , USA
6. Danish Headache Center, Department of Neurology , University of Copenhagen, Rigshospitalet Glostrup , Glostrup , Denmark
7. Department of Occupational and Social Medicine , Holbaek Hospital, University of Copenhagen , Holbaek , Denmark