title: Framing of mobility items: a source of poor agreement between preference-based health-related quality of life instruments in a population of individuals receiving assisted ventilation.
abstract: To explore the influence of descriptive differences in items evaluating mobility on index scores generated from two generic preference-based health-related quality of life (HRQoL) instruments.
  
  
  
  The study examined cross-sectional data from a postal survey of individuals receiving assisted ventilation in two state/province-wide home mechanical ventilation services, one in British Columbia, Canada and the other in Victoria, Australia. The Assessment of Quality of Life 8-dimension (AQoL-8D) and the EQ-5D-5L were included in the data collection. Graphical illustrations, descriptive statistics, and measures of agreement [intraclass correlation coefficients (ICCs) and Bland-Altman plots] were examined using index scores derived from both instruments. Analyses were performed on the full sample as well as subgroups defined according to respondents' self-reported ability to walk.
  
  
  
  Of 868 individuals receiving assisted ventilation, 481 (55.4%) completed the questionnaire. Mean index scores were 0.581 (AQoL-8D) and 0.566 (EQ-5D-5L) with 'moderate' agreement demonstrated between the two instruments (ICC = 0.642). One hundred fifty-nine (33.1%) reported level 5 ('I am unable to walk about') on the EQ-5D-5L Mobility item. The walking status of respondents had a marked influence on the comparability of index scores, with a larger mean difference (0.206) and 'slight' agreement (ICC = 0.386) observed when the non-ambulant subgroup was evaluated separately.
  
  
  
  This study provides further evidence that between-measure discrepancies between preference-based HRQoL instruments are related in part to the framing of mobility-related items. Longitudinal studies are necessary to determine the responsiveness of preference-based HRQoL instruments in cohorts that include non-ambulant individuals.
authors.affiliation: Institute for Breathing and Sleep, Austin Health, PO Box 5555, Heidelberg, VIC, 3084, Australia. liam.hannan@austin.org.au.|Department of Respiratory and Sleep Medicine, Austin Health, Victoria, Australia. liam.hannan@austin.org.au.|Medicine, Dentistry, and Health Science, University of Melbourne, Victoria, Australia. liam.hannan@austin.org.au.|Victorian Respiratory Support Service, Austin Health, Victoria, Australia. liam.hannan@austin.org.au.
authors.forename: Liam M
authors.initials: LM
authors.lastname: Hannan
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, Burnaby, BC, Canada.|International Collaboration on Repair Discoveries (ICORD), Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.|Centre for Clinical Epidemiology and Evaluation, Vancouver Coastal Health Research Institute, Vancouver, BC, Canada.
authors.forename: David G T
authors.initials: DGT
authors.lastname: Whitehurst
authors.affiliation: Centre for Clinical Epidemiology and Evaluation, Vancouver Coastal Health Research Institute, Vancouver, BC, Canada.|School of Population and Public Health, University of British Columbia, Vancouver, BC, Canada.|Health Economics Research Unit, University of Aberdeen, Aberdeen, Scotland, UK.
authors.forename: Stirling
authors.initials: S
authors.lastname: Bryan
authors.affiliation: Department of Medicine, University of British Columbia, Vancouver, BC, Canada.|Provincial Respiratory Outreach Program, Vancouver, BC, Canada.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Road
authors.affiliation: Institute for Breathing and Sleep, Austin Health, PO Box 5555, Heidelberg, VIC, 3084, Australia.|Department of Respiratory and Sleep Medicine, Austin Health, Victoria, Australia.|Medicine, Dentistry, and Health Science, University of Melbourne, Victoria, Australia.|Victorian Respiratory Support Service, Austin Health, Victoria, Australia.
authors.forename: Christine F
authors.initials: CF
authors.lastname: McDonald
authors.affiliation: Institute for Breathing and Sleep, Austin Health, PO Box 5555, Heidelberg, VIC, 3084, Australia.|Department of Respiratory and Sleep Medicine, Austin Health, Victoria, Australia.|Medicine, Dentistry, and Health Science, University of Melbourne, Victoria, Australia.|Victorian Respiratory Support Service, Austin Health, Victoria, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Berlowitz
authors.affiliation: Institute for Breathing and Sleep, Austin Health, PO Box 5555, Heidelberg, VIC, 3084, Australia.|Department of Respiratory and Sleep Medicine, Austin Health, Victoria, Australia.|Medicine, Dentistry, and Health Science, University of Melbourne, Victoria, Australia.|Victorian Respiratory Support Service, Austin Health, Victoria, Australia.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Howard
mesh_terms: D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life / Q000523:psychology*; D012121:Respiration, Artificial / Q000379:methods*
keywords: AQoL-8D; EQ-5D-5L; Mobility; Non-invasive ventilation; Quality of life; Respiratory insufficiency