Correction: A Proposal for a Comprehensive Grading of Parkinson's Disease Severity Combining Motor and Non-Motor Assessments: Meeting an Unmet Need

• Kallol Ray Chaudhuri, 
• Jose Manuel Rojo, 
• Anthony H. V. Schapira, 
• David J. Brooks, 
• Fabrizio Stocchi, 
• Per Odin, 
• Angelo Antonini, 
• Richard G. Brown, 
• Pablo Martinez-Martin