Epidemiology of Parkinsonism

Epidemiology is the study of large numbers of individuals to ascertain incidence, life expectancy, prevalence, time trends, preceding and associated illnesses, and other factors in a disease. Contrasted to laboratory studies in which the experimental conditions can be controlled, epidemiology examines natural events that may have been influenced by health care, economic, and social factors. Epidemiology is broadly divided into four categories—descriptive, analytic, clinical, and experimental—although there is considerable overlap (1). Descriptive epidemiology deals with incidence, age and sex distribution, life expectancy, and prevalence rates. Analytic epidemiology is aimed at identifying factors that are positively or negatively associated with the illness and hence may be causally linked. Because the events that significantly influence the epidemiology of a disease cannot be controlled, it is important that any bias that may confound the observations be identified and avoided or adjusted for. Clinical epidemiology includes studies that require repeated clinical assessments and/or pathological studies to determine disease profile. Hypotheses generated by descriptive and analytic epidemiology may be tested with these studies. Experimental