title: An examination of Alzheimer's disease case definitions using Medicare claims and survey data.
abstract: BACKGROUND
  The prevalence and expenditure estimates of Alzheimer's disease (AD) from studies using one data source to define cases vary widely. The objectives of this study were to assess agreement between AD case definitions classified with Medicare claims and survey data and to provide insight into causes of widely varied expenditure estimates.
  
  
  METHODS
  Data were obtained from the 1999-2004 Medicare Current Beneficiary Survey linked with Medicare claims (n = 57,669). Individuals with AD were identified by survey, diagnosis, use of an AD prescription medicine, or some combination thereof. We also explored how much health care and drug expenditures vary by AD case definition.
  
  
  RESULTS
  The prevalence of AD differed significantly by case definition. Using survey report alone yielded more cases (n = 1,994 or 3.46%) than diagnosis codes alone (n = 1,589 or 2.76%) or Alzheimer's medication use alone (n = 1,160 or 2.01%). Agreement between case definitions was low, with kappa coefficients ranging from 0.37 to 0.40. Per capita health expenditures ranged from $16,547 to $24,937, and drug expenditures ranged from $2,303 to $3,519, depending on how AD was defined.
  
  
  CONCLUSIONS
  Different information sources yield widely varied prevalence and expenditure estimates. Although claims data provided a more objective means for identifying AD cases, survey report identified more cases, and pharmacy data also are an important source for case ascertainment. Using any single source will underestimate the prevalence and associated cost of AD. The wide range of AD cases identified by using different data sources demands caution interpreting cost-of-illness studies using single data sources.
authors.affiliation: Center for the Evaluation of Value and Risk in Health, Institute for Clinical Research and Health Policy Studies, Tufts Medical Center, Boston, MA, USA. plin@tuftsmedicalcenter.org
authors.forename: Pei-Jung
authors.initials: PJ
authors.lastname: Lin
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Kaufer
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Maciejewski
authors.forename: Rahul
authors.initials: R
authors.lastname: Ganguly
authors.forename: John E
authors.initials: JE
authors.lastname: Paul
authors.forename: Andrea K
authors.initials: AK
authors.lastname: Biddle
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000145:classification* / Q000191:economics / Q000453:epidemiology; D017281:Cost of Illness; D005260:Female; D006291:Health Policy; D006801:Humans; D007345:Insurance Claim Review / Q000191:economics / Q000706:statistics & numerical data; D008297:Male; D006278:Medicare / Q000191:economics* / Q000706:statistics & numerical data*; D016344:Medicare Part A / Q000191:economics / Q000706:statistics & numerical data; D018697:Nootropic Agents / Q000627:therapeutic use; D011785:Quality Assurance, Health Care; D012959:Socioeconomic Factors; D009626:Terminology as Topic; D014481:United States / Q000453:epidemiology
chemical_list: D018697:Nootropic Agents