Sample selection and the natural history of disease. Studies of febrile seizures.

We have compared published reports on the frequency of unfavorable sequelae in a common disorder of childhood, febrile seizures, as ascertained from hospital clinics or referral units, with the frequency as reported from population-based studies. Studies on defined populations, in which the attempt was made to recognize and follow up all affected persons regardless of medical care sought for the condition, are in close agreement and indicate relatively low rates of unfavorable sequelae. Clinic-based studies of febrile seizures have reported disparate results, including high frequencies of adverse outcomes. A possible explanation is that patients in clinic-based studies may not be representative of persons with the disorder in the general population.