1. Department of Neurology, Perelman School of Medicine University of Pennsylvania Philadelphia Pennsylvania USA
2. Translational Center of Excellence for Neuroepidemiology and Neurology Outcomes Research, Perelman School of Medicine University of Pennsylvania Philadelphia Pennsylvania USA
3. Center for Clinical Epidemiology and Biostatistics University of Pennsylvania Philadelphia Pennsylvania USA
4. Department of Ophthalmology, Perelman School of Medicine University of Pennsylvania Philadelphia Pennsylvania USA
5. Division of Neurology, Department of Medicine University of Toronto Toronto Ontario Canada
6. Morton and Gloria Shulman Movement Disorders Centre and the Edmond J. Safra Program in Parkinson's Disease Research Toronto Western Hospital and University of Toronto Toronto Ontario Canada
7. Leonard Davis Institute for Health Economics University of Pennsylvania Philadelphia Pennsylvania USA