title: A Vision "Bolt-On" Item Could Increase the Discriminatory Power of the EQ-5D Index Score.
abstract: BACKGROUND
  Recently, a vision "bolt-on" EuroQol five-dimensional questionnaire (EQ-5D) was developed and tentative utility values (i.e., a "value set") for this new descriptive system were estimated.
  
  
  OBJECTIVE
  To compare the discriminatory power of this bolt-on and standard utility-based EQ-5D health indices.
  
  
  METHODS
  Cross-sectional data on the (3-level) vision bolt-on EQ-5D were collected through face-to-face interviews with 500 and 336 individuals with and without visual impairment, respectively. To assess the discriminatory power of the vision bolt-on index relative to the standard EQ-5D index developed in the vision bolt-on valuation study, 16 pairs of mutually exclusive subgroups of individuals defined by the individuals' visual acuity and responses to the 14-item visual function questionnaire were compared pairwise. The absolute mean difference in the two index scores and the corresponding F statistic derived from the comparisons were used as measures of discriminatory power.
  
  
  RESULTS
  The absolute mean difference in the bolt-on index score was larger than that in the standard EQ-5D index score in 14 of the 16 comparisons. The bolt-on index score exhibited a larger F-statistic value than did the standard EQ-5D index score in all known-group comparisons, with the F-statistic ratio ranging from 0.415 to 0.770.
  
  
  CONCLUSIONS
  The vision bolt-on EQ-5D appears to be more discriminative than the standard EQ-5D in measurement of vision problems. Future studies should investigate the extent to which the vision bolt-on item can increase the sensitivity of the EQ-5D to vision change in interventional studies.
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, Singapore. Electronic address: ephln@nus.edu.sg.
authors.forename: Nan
authors.initials: N
authors.lastname: Luo
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, Singapore.
authors.forename: Xingzhi
authors.initials: X
authors.lastname: Wang
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.
authors.forename: Marcus
authors.initials: M
authors.lastname: Ang
authors.affiliation: Duke-NUS Graduate Medical School, Singapore.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Finkelstein
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Ophthalmology, National University Health System and National University of Singapore, Singapore.
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Ophthalmology, National University Health System and National University of Singapore, Singapore.
authors.forename: Tien-Yin
authors.initials: TY
authors.lastname: Wong
authors.affiliation: Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Duke-NUS Graduate Medical School, Singapore; Department of Ophthalmology, National University Health System and National University of Singapore, Singapore; Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, Melbourne, Australia.
authors.forename: Ecosse
authors.initials: E
authors.lastname: Lamoureux
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D003627:Data Interpretation, Statistical; D006305:Health Status Indicators; D006801:Humans; D007407:Interviews as Topic; D008875:Middle Aged; D011788:Quality of Life; D012720:Severity of Illness Index; D012846:Singapore; D011795:Surveys and Questionnaires / Q000592:standards*; D014786:Vision Disorders / Q000523:psychology*
keywords: EQ-5D; bolt-on; discriminatory power; vision problems; visual impairment