1. Department of Neurology, University of Texas Southwestern Medical Center, Dallas, TX, USA
2. North Texas Institute of Neurology & Headache, Plano, TX, USA
3. Neurology Center of San Antonio, Dallas, TX, USA
4. Department of Biostatistics, Section on Research Methods and Clinical Trials, University of Alabama at Birmingham, Birmingham, AL, USA
5. Neurology Section, VA North Texas Health Care System, Dallas, TX, USA