Epidemiology and the extent of mental retardation.

Drawing firm conclusions from various findings of epidemiologic research in the mental retardation field is fraught with seemingly endless frustration and confusion. There have been so many studies in different countries on various sized populations with dissimilar methodologies, and concepts and conditions often have been defined differently. Results from various surveys too often lack congruity, and sometimes findings are not reported until several years after the data are collected. However, these criticisms of epidemiologic studies are not meant to suggest that they are worthless or that investigators have been incompetent. Each was attempting to examine different features of particular populations under diverse circumstances, with varying resources and measurement tools, and with distinct goals in mind. It is safe to say that attempting to compare or generalize information collected in one geographic location with another can be very difficult and often unwise. If one intends to plan rationally the services for a particular geographic area, then one must use data that are derived from the population in that area. Finally, results from epidemiologic surveys have been useful in educating professionals and the general public about the extent of problems presented and experienced by persons with mental retardation. As well, this information has proved essential for properly planning and prioritizing the need for services of a diagnostic, treatment, prevention, and research nature. To improve epidemiologic research in the future, it is hoped that coordinated, multipurpose, nationwide, and international data reporting systems for the collection of uniform mental health-mental retardation data can be developed.