title: Post hoc Parkinson's disease: identifying an uncommon disease in the Cardiovascular Health Study.
abstract: BACKGROUND
  Although ongoing cohort studies offer a unique opportunity to apply existing information collected prospectively to further the scientific understanding of Parkinson's disease (PD), they typically have limited information for clinical diagnosis.
  
  
  METHODS
  We used combinations of self-report, International Classification of Diseases - 9th edition codes and antiparkinsonian medications to identify PD in the Cardiovascular Health Study. To determine whether the expected inverse association between smoking and PD is evident using our outcome definitions, we assessed baseline smoking characteristics for various definitions of PD.
  
  
  RESULTS
  We identified 60 cases with prevalent PD (1.0%; 95% confidence interval, CI = 0.8-1.3%) and 154 with incident PD by year 14. Clear associations were observed for current smokers (odds ratio, OR = 0.50; 95% CI = 0.26-0.95) and for those who smoked ≥50 pack-years (OR = 0.53; 95% CI = 0.29-0.96). Estimates for smoking were similar when ≥2 data sources were required. Estimates for self-report alone were attenuated towards null.
  
  
  CONCLUSIONS
  Using multiple data sources to identify PD represents an alternative method of outcome identification in a cohort that would otherwise not be possible for PD research. Ongoing cohort studies can provide settings in which rapid replication and explorations of new hypotheses for PD are possible.
authors.affiliation: Department of Neurology, School of Medicine, University of Washington, Seattle, WA 98125, USA. thanhton@uw.edu
authors.forename: T G
authors.initials: TG
authors.lastname: Ton
authors.forename: S
authors.initials: S
authors.lastname: Jain
authors.forename: R
authors.initials: R
authors.lastname: Boudreau
authors.forename: E L
authors.initials: EL
authors.lastname: Thacker
authors.forename: E S
authors.initials: ES
authors.lastname: Strotmeyer
authors.forename: A B
authors.initials: AB
authors.lastname: Newman
authors.forename: W T
authors.initials: WT
authors.lastname: Longstreth
authors.forename: H
authors.initials: H
authors.lastname: Checkoway
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002319:Cardiovascular System; D015331:Cohort Studies; D005260:Female; D006304:Health Status; D006801:Humans; D015994:Incidence; D008297:Male; D016017:Odds Ratio; D010300:Parkinson Disease / Q000453:epidemiology*; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology