title: Construction of the descriptive system for the Assessment of Quality of Life AQoL-6D utility instrument.
abstract: BACKGROUND
  Multi attribute utility (MAU) instruments are used to include the health related quality of life (HRQoL) in economic evaluations of health programs. Comparative studies suggest different MAU instruments measure related but different constructs. The objective of this paper is to describe the methods employed to achieve content validity in the descriptive system of the Assessment of Quality of Life (AQoL)-6D, MAU instrument.
  
  
  METHODS
  The AQoL program introduced the use of psychometric methods in the construction of health related MAU instruments. To develop the AQoL-6D we selected 112 items from previous research, focus groups and expert judgment and administered them to 316 members of the public and 302 hospital patients. The search for content validity across a broad spectrum of health states required both formative and reflective modelling. We employed Exploratory Factor Analysis and Structural Equation Modelling (SEM) to meet these dual requirements.
  
  
  CONCLUSIONS
  The resulting instrument employs 20 items in a multi-tier descriptive system. Latent dimension variables achieve sensitive descriptions of 6 dimensions which, in turn, combine to form a single latent QoL variable. Diagnostic statistics from the SEM analysis are exceptionally good and confirm the hypothesised structure of the model.
  
  
  CONCLUSIONS
  The AQoL-6D descriptive system has good psychometric properties. They imply that the instrument has achieved construct validity and provides a sensitive description of HRQoL. This means that it may be used with confidence for measuring health related quality of life and that it is a suitable basis for modelling utilities for inclusion in the economic evaluation of health programs.
authors.affiliation: Centre for Health Economics, Monash University, Wellington Road, Clayton, VIC 3800, Australia. Jeffrey.Richardson@monash.edu
authors.forename: Jeffrey R J
authors.initials: JR
authors.lastname: Richardson
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Peacock
authors.forename: Graeme
authors.initials: G
authors.lastname: Hawthorne
authors.forename: Angelo
authors.initials: A
authors.lastname: Iezzi
authors.forename: Gerald
authors.initials: G
authors.lastname: Elsworth
authors.forename: Neil A
authors.initials: NA
authors.lastname: Day
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001315:Australia; D005163:Factor Analysis, Statistical; D005260:Female; D017144:Focus Groups; D017408:Guidelines as Topic; D006305:Health Status Indicators; D006801:Humans; D007297:Inpatients / Q000523:psychology / Q000706:statistics & numerical data; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D010045:Outpatients / Q000523:psychology / Q000706:statistics & numerical data; D015397:Program Evaluation; D011594:Psychometrics / Q000295:instrumentation* / Q000379:methods; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires / Q000191:economics; D014218:Triage