title: Validity of dementia and Alzheimer's disease diagnoses in Finnish national registers.
abstract: BACKGROUND
  We investigated dementia and Alzheimer disease (AD) diagnoses in three national registers in Finland: the Hospital Discharge Register (HDR), the Drug Reimbursement Register, and the Causes of Death Register (CDR).
  
  
  METHODS
  The Cardiovascular Risk Factors, Aging and Dementia (CAIDE) study was used as the gold standard. Participants were first evaluated in 1972 to 1987, and were reexamined in 1998 and in 2005 to 2008.
  
  
  RESULTS
  Two approaches were used for the HDR: with a time restriction (considering "positive" only those cases recorded in the HDR before CAIDE study evaluations) and without a time restriction. Sensitivity of the HDR was 13.7% with time restriction and 51% without time restriction (dementia), and 15.6% with time restriction 55.6% without time restriction (AD). The positive predictive value (PPV) was 87.5% with time restriction and 96.3% without time restriction (dementia), and 100% for AD. Sensitivity and PPV of the HDR were greater after 1998. For AD in the Drug Reimbursement Register alone, sensitivity was 63.5% and PPV was 97.1%; together with the HDR, sensitivity became 65.4% with time restriction and 71.1% without time restriction, and PPV was 100%. For dementia in the CDR, sensitivity was 62.2% and PPV was 100%.
  
  
  CONCLUSIONS
  Diagnoses in registers have very good accuracy, but underestimation of dementia/AD occurrence may cause an underestimation of associations with risk/protective factors.
authors.affiliation: Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland; Aging Research Center, Karolinska Institutet, Stockholm, Sweden; Karolinska Institutet Alzheimer Disease Research Center, Stockholm, Sweden. Electronic address: alina.solomon@uef.fi.
authors.forename: Alina
authors.initials: A
authors.lastname: Solomon
authors.affiliation: Karolinska Institutet Alzheimer Disease Research Center, Stockholm, Sweden; Department of Chronic Disease Prevention, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Tiia
authors.initials: T
authors.lastname: Ngandu
authors.affiliation: Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland; Department of Neurology, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Hilkka
authors.initials: H
authors.lastname: Soininen
authors.affiliation: Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland.
authors.forename: M Merja
authors.initials: MM
authors.lastname: Hallikainen
authors.affiliation: Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland; Aging Research Center, Karolinska Institutet, Stockholm, Sweden; Karolinska Institutet Alzheimer Disease Research Center, Stockholm, Sweden; Department of Chronic Disease Prevention, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Miia
authors.initials: M
authors.lastname: Kivipelto
authors.affiliation: Department of Chronic Disease Prevention, National Institute for Health and Welfare, Helsinki, Finland; Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland; Hospital District of North Karelia, Joensuu, Finland.
authors.forename: Tiina
authors.initials: T
authors.lastname: Laatikainen
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000175:diagnosis*; D003704:Dementia / Q000175:diagnosis*; D005260:Female; D005387:Finland; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D012042:Registries; D012680:Sensitivity and Specificity
keywords: Alzheimer disease; Dementia; Diagnosis; Epidemiology; Population-based registers