Incidence and prevalence studies in epilepsy and their methodological problems: a review.

Epidemiological studies in epilepsy have a number of specific problems, discussed here with reference to the published literature. Case ascertainment may pose difficulties because of deficiencies in patients reporting and in the diagnosis of seizures, and inherent methodological problems; the classification of epilepsy is often arbitrary and definitions variable; unsuspected selection bias may markedly influence incidence and prevalence rates. The major published incidence and prevalence studies are reviewed and the factors influencing these rates discussed.