1. Laboratory of Parkinson Disease and Other Neurodegenerative Movement Disorders, Clinical and Experimental Research, Department of Neurology, Hospital Clínic of Barcelona; Institut d'Investigacions Biomèdiques August Pi i Sunyer, University of Barcelona; Barcelona Spain
2. Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas; Madrid Spain
3. Movement Disorders Unit, Department of Neurology, Hospital Clínic de Barcelona; Institut d'Investigacions Biomèdiques August Pi i Sunyer, University of Barcelona; Barcelona Spain
4. Movement Disorders Unit, Department of Neurology; Hospital Universitario Marqués de Valdecilla, Universidad de Cantabria; Santander Spain
5. Medical Statistics Core Facility, Institut d'Investigacions Biomèdiques August Pi i Sunyer and Hospital Clinic; Barcelona Spain
6. Biostatistics Unit, Faculty of Medicine, Universitat Autònoma de Barcelona; Barcelona Spain