title: Defining incident cases of epilepsy in administrative data.
abstract: OBJECTIVE
  To determine the minimum enrollment duration for identifying incident cases of epilepsy in administrative data.
  
  
  METHODS
  We performed a retrospective dynamic cohort study using Ohio Medicaid data from 1992 to 2006 to identify a total of 5037 incident epilepsy cases who had at least 1 year of follow-up prior to epilepsy diagnosis (epilepsy-free interval). The incidence for epilepsy-free intervals from 1 to 8 years, overall and stratified by pre-existing disability status, was examined. The graphical approach between the slopes of incidence estimates and the epilepsy-free intervals was used to identify the minimum epilepsy-free interval that minimized misclassification of prevalent as incident epilepsy cases.
  
  
  RESULTS
  As the length of epilepsy-free interval increased, the incidence rates decreased. A graphical plot showed that the decline in incidence of epilepsy became nearly flat beyond the third epilepsy-free interval.
  
  
  CONCLUSIONS
  The minimum of 3-year epilepsy-free interval is needed to differentiate incident from prevalent cases in administrative data. Shorter or longer epilepsy-free intervals could result in over- or under-estimation of epilepsy incidence.
authors.affiliation: Department of Epidemiology & Biostatistics, Case Western Reserve University, Cleveland, OH, United States.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Bakaki
authors.forename: Siran M
authors.initials: SM
authors.lastname: Koroukian
authors.forename: Leila W
authors.initials: LW
authors.lastname: Jackson
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Albert
authors.forename: Kitti
authors.initials: K
authors.lastname: Kaiboriboon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000927:Anticonvulsants / Q000627:therapeutic use; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D004185:Disability Evaluation; D004827:Epilepsy / Q000145:classification / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008484:Medicaid / Q000458:organization & administration / Q000706:statistics & numerical data; D008875:Middle Aged; D009820:Ohio / Q000453:epidemiology; D015995:Prevalence; D012189:Retrospective Studies; D009626:Terminology as Topic; D014481:United States; D055815:Young Adult
chemical_list: D000927:Anticonvulsants
keywords: Administrative data; Epilepsy; Incidence