1. Department of Neurology, University of Essen, Essen, Germany
2. Department of Neurology, Tbilisi Medical University, Tbilisi, Georgia
3. School of Public Health, Tbilisi Medical University, Tbilisi, Georgia
4. NGO, ‘Partnership in Research and Action for Health’, Tbilisi, Georgia
5. Danish Headache Centre, Glostrup University, Copenhagen, Denmark
6. Norwegian National Headache Centre, Department of Neuroscience, Norwegian University of Science and Technology, and St Olavs Hospital, Trondheim, Norway
7. Division of Neuroscience and Mental Health, Imperial College London, London, UK