A number of collaborative efforts involve the investigation of the characteristics of unusual or less debilitating (e.g., headache) neurologic disease phenomena. Unusual associations or space/time clusters of neurologic disorders may provide leads to etiology or therapy. These may be tested through more formal approaches. Surveys of prevalence and natural history and a case-control study of progressive supranuclear palsy (PSP) have been completed in two counties in New Jersey. The point prevalence was 1.39/1 00,000. The median intervals to onset of requiring assistance was 3.1 years and to death, 9.7 years. The case-control study did not implicate a history of stroke, hypertension or smoking as risk factors for PSP. A prevalence survey of migraine in the People's Republic of China yielded a point prevalence ratio of 690/100,000, and indicated that the prevalence ratio for females was higher than that for males.
