Epidemiology of Parkinson's disease.

Epidemiological research aims to provide information on the development, prevalence and progression of diseases, and their associated risk factors. Epidemiological research is thus the basis of increasing our understanding on the aetiology of diseases and as a consequence the starting point for identifying at risk groups in the population, development for novel prevention and treatment strategies, and health care planning. This review provides an overview of the epidemiology of Parkinson's disease, the second most common neurodegenerative disorder, with special emphasis on population-based data on the clinical progression of motor and non-motor features of the disease.