Prevalence surveys of neurologic disorders: methodologic implications of the Copiah County Study.

This article addresses three questions to be answered during the planning of prevalence surveys of chronic disorders in geographically defined populations: (a) Should personal interviews be used alone (i.e. without accompanying physical examinations) to find and confirm cases in a household population? (b) As an alternative means of identifying cases, is it adequate to review patient records from hospitals and clinics serving the population to be surveyed? (c) Should population members residing in institutions of long-term care be made ineligible for the anticipated survey? Data on major neurologic disorders, obtained from the Copiah County Study, are used to suggest caution in answering any of these questions in the affirmative, since in particular circumstances the consequences for the intended research may be serious or even disastrous. For example, with 42% of Parkinson's disease cases diagnosed for the first time during the study, a casefinding approach solely through medical-care providers would have been highly questionable for that disorder.