title: Developing a dementia-specific health state classification system for a new preference-based instrument AD-5D.
abstract: BACKGROUND
  With an ageing population, the number of people with dementia is rising. The economic impact on the health care system is considerable and new treatment methods and approaches to dementia care must be cost effective. Economic evaluation requires valid patient reported outcome measures, and this study aims to develop a dementia-specific health state classification system based on the Quality of Life for Alzheimer's disease (QOL-AD) instrument (nursing home version). This classification system will subsequently be valued to generate a preference-based measure for use in the economic evaluation of interventions for people with dementia.
  
  
  METHODS
  We assessed the dimensionality of the QOL-AD to develop a new classification system. This was done using exploratory and confirmatory factor analysis and further assessment of the structure of the measure to ensure coverage of the key areas of quality of life. Secondly, we used Rasch analysis to test the psychometric performance of the items, and select item(s) to describe each dimension. This was done on 13 items of the QOL-AD (excluding two general health items) using a sample of 284 residents living in long-term care facilities in Australia who had a diagnosis of dementia.
  
  
  RESULTS
  A five dimension classification system is proposed resulting from the three factor structure (defined as 'interpersonal environment', 'physical health' and 'self-functioning') derived from the factor analysis and two factors ('memory' and 'mood') from the accompanying review. For the first three dimensions, Rasch analysis selected three questions of the QOL-AD ('living situation', 'physical health', and 'do fun things') with memory and mood questions representing their own dimensions. The resulting classification system (AD-5D) includes many of the health-related quality of life dimensions considered important to people with dementia, including mood, global function and skill in daily living.
  
  
  CONCLUSIONS
  The development of the AD-5D classification system is an important step in the future application of the widely used QOL-AD in economic evaluations. Future valuation studies will enable this tool to be used to calculate quality adjusted life years to evaluate treatments and interventions for people diagnosed with mild to moderate dementia.
authors.affiliation: Center for Applied Health Economics, Menzies Health Institute Queensland, Griffith University, Nathan, QLD, 4111, Australia. kim.nguyen@griffith.edu.au.|The NHMRC Cognitive Decline Partnership Centre, Sydney, Australia. kim.nguyen@griffith.edu.au.
authors.forename: Kim-Huong
authors.identifier: http://orcid.org/0000-0002-2592-9372
authors.initials: KH
authors.lastname: Nguyen
authors.affiliation: Centre for Health Economics Research and Evaluation, University of Technology Sydney, Sydney, Australia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Mulhern
authors.affiliation: Center for Applied Health Economics, Menzies Health Institute Queensland, Griffith University, Nathan, QLD, 4111, Australia.
authors.forename: Sanjeewa
authors.initials: S
authors.lastname: Kularatna
authors.affiliation: Center for Applied Health Economics, Menzies Health Institute Queensland, Griffith University, Nathan, QLD, 4111, Australia.
authors.forename: Joshua
authors.initials: J
authors.lastname: Byrnes
authors.affiliation: Centre for Health Practice Innovation, Griffith University, Brisbane, Australia.
authors.forename: Wendy
authors.initials: W
authors.lastname: Moyle
authors.affiliation: Center for Applied Health Economics, Menzies Health Institute Queensland, Griffith University, Nathan, QLD, 4111, Australia.|The NHMRC Cognitive Decline Partnership Centre, Sydney, Australia.|Metro North Hospital and Health Service District, Brisbane, Australia.
authors.forename: Tracy
authors.initials: T
authors.lastname: Comans
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000145:classification* / Q000175:diagnosis* / Q000523:psychology / Q000628:therapy; D001315:Australia; D003704:Dementia / Q000145:classification* / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D006305:Health Status Indicators; D006707:Homes for the Aged; D006801:Humans; D008297:Male; D008875:Middle Aged; D009735:Nursing Homes; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*
keywords: Dementia; Economic evaluation; Health state classification; Health-related quality of life; Preference-based measure; QALY; QOL-AD