Descriptive epidemiology of Parkinson's disease: disease distribution and hypothesis formulation.

In the last 30 years, there have been several studies reporting morbidity rates for PD. Age-adjusted prevalence ratios from these investigations range from a low of 30/100,000 to a high of 180/100,000. Data from one population (Rochester, Minnesota) indicate virtually no change in the incidence rates in 35 years. In general, reported prevalence figures have been higher among Caucasians when compared to black or Oriental populations. Studies show an increasing prevalence ratio with age, and many reveal a higher risk for men. However, these investigations usually relied on records of health care providers (mainly hospitals and medical practitioners) in the identification of cases. Excluded from the resulting morbidity data are individuals who failed to seek medical attention for their symptoms or individuals who were improperly diagnosed. Among the various investigations, the differences in study methods, levels of case ascertainment, and definitions of PD could account for the variation in the reported morbidity estimates. To minimize these problems, a standard methodology using a door-to-door survey technique and uniform diagnostic criteria was developed. This study design was implemented in surveys conducted in a biracial population (blacks and whites) in the United States and in urban populations of the People's Republic of China and is currently being carried out in Nigeria. In contrast to earlier investigations, the U. S. study revealed no substantial differences in age-adjusted prevalence ratios by race. The prevalence ratios derived from the sample population of 63,195 in urban areas of China are lower than the U. S. figures based on the same methods of case identification.(ABSTRACT TRUNCATED AT 250 WORDS)