1. World Health Organization (1980) International classification of impairments, disabilities, and handicaps. World Health Organization, Geneva
2. World Health Organization (2002) Towards a common language for functioning, disability and health. World Health Organization, Geneva
3. Schwab RS, England AC (1969) Projection technique for evaluating surgery in Parkinson’s disease. In: Gillingham FJ, Donaldson MC (eds) Third symposium on Parkinson’s disease. E & S Livingston, Edinburgh, pp 152–157
4. Wade DT, Collin C (1988) The Barthel ADL Index: a standard measure of physical disability? Int Disabil Stud 10(2):64–67
5. Hoehn MM, Yahr MD (1967) Parkinsonism: onset, progression, and mortality. Neurology 17(5):427–442