1. Institute for Medical Informatics, Biometry, and Epidemiology, Medical Faculty of the University Duisburg-Essen, Essen, Germany
2. New England Institute for Neurology and Headache, Stamford, CT, USA
3. Headache Center North-East, Department of Neurology, University Medical Center Rostock, Rostock, Germany
4. Teva Branded Pharmaceutical Products R&D, Inc., West Chester, PA, USA
5. Jefferson Headache Center, Philadelphia, PA, USA