title: Deriving population norms for the AQoL-6D and AQoL-8D multi-attribute utility instruments from web-based data.
abstract: (i) to demonstrate a method which ameliorates the problem of self-selection in the estimation of population norms from web-based data and (ii) to use the method to calculate population norms for two multi-attribute utility (MAU) instruments, the AQoL-6D and AQoL-8D, and population norms for the sub-scales from which they are constructed.
  
  
  
  A web-based survey administered the AQoL-8D MAU instrument (which subsumes the AQoL-6D questionnaire), to members of the public along with the AQoL-4D which has extant population norms. Age, gender and the AQoL-4D were used as post-stratification auxiliary variables to construct weights to ameliorate the potential effects of self-selection associated with web-based surveys. The weights were used to estimate unbiased population norms. Standard errors from the weighted samples were calculated using Jackknife estimation.
  
  
  
  For both AQoL-6D and AQoL-8D, physical health dimensions decline significantly with age. In contrast, for the majority of the psycho-social dimensions there is a significant U-shaped profile. The net effect is a shallow U-shaped relationship between age and both the AQoL-6D and AQoL-8D utilities. This contrasts with the almost monotonic decline in the utilities derived from the AQoL-4D and SF-6D MAU instruments.
  
  
  
  Post-stratification weights were used to ameliorate potential bias in the derivation of norms from web-based data for the AQoL-6D and AQoL-8D. The methods may be used generally to obtain norms when suitable auxiliary variables are available. The inclusion of an enlarged psycho-social component in the two instruments significantly alters the demographic profile.
authors.affiliation: Centre for Health Economics, Monash Business School, Monash University, Melbourne, Australia.
authors.forename: Aimee
authors.initials: A
authors.lastname: Maxwell
authors.affiliation: Department of Econometrics and Business Statistics, Monash Business School, Monash University, Melbourne, Australia.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Özmen
authors.affiliation: Centre for Health Economics, Monash Business School, Monash University, Melbourne, Australia.
authors.forename: Angelo
authors.initials: A
authors.lastname: Iezzi
authors.affiliation: Centre for Health Economics, Monash Business School, Monash University, Melbourne, Australia. jeffrey.richardson@monash.edu.
authors.forename: Jeff
authors.initials: J
authors.lastname: Richardson
mesh_terms: D000328:Adult; D016208:Databases, Factual / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D055815:Young Adult
keywords: AQoL; CUA; Multi-attribute utility; Norms; QoL