title: An exploratory study to test the impact on three "bolt-on" items to the EQ-5D.
abstract: BACKGROUND
  Generic preference-based measures were criticized for being inappropriate in some conditions. One solution is to include "bolt-on" dimensions describing additional specific health problems.
  
  
  OBJECTIVE
  This study aimed to develop bolt-on dimensions to the EuroQol five-dimensional questionnaire (EQ-5D) and assess their impact on health state values.
  
  
  METHODS
  Bolt-on dimensions were developed for vision problems, hearing problems, and tiredness. Each bolt-on dimension had three severity levels to match the EQ-5D. Three "core" EQ-5D states across a range of severity were selected, and each level of a bolt-on item was added, resulting in nine states in each condition. Health states with and without the bolt-on dimensions were valued by 300 members of the UK general public using time trade-off in face-to-face interviews, and mean health state values were compared using t tests. Regression analysis examined the impact of the bolt-on variants and the level of the bolt-on items after controlling for sociodemographic characteristics.
  
  
  RESULTS
  Bolt-on dimensions had an impact on health state values of the EQ-5D; however, the size, direction, and significance of the impact depend on the severity of the core EQ-5D state and of the bolt-on dimension. Regression analysis demonstrated that after controlling for possible differences in sociodemographic characteristics between the groups, there were no significant differences in health state values between the three bolt-on dimensions but confirmed that the impact depended on the severity of the EQ-5D health state and the levels of bolt-on dimensions.
  
  
  CONCLUSIONS
  The impact of a bolt-on dimension on the EQ-5D depends on the core health state and the level of the bolt-on dimension. Further research in this area is encouraged.
authors.affiliation: Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK. Electronic address: yaling.yang@phc.ox.ac.uk.
authors.forename: Yaling
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Health Economics and Decision Science, School of Health and Related Research, University of Sheffield, Sheffield, UK.
authors.forename: Donna
authors.initials: D
authors.lastname: Rowen
authors.affiliation: Health Economics and Decision Science, School of Health and Related Research, University of Sheffield, Sheffield, UK.
authors.forename: John
authors.initials: J
authors.lastname: Brazier
authors.affiliation: Health Economics and Decision Science, School of Health and Related Research, University of Sheffield, Sheffield, UK; Department of Economics, University of Sheffield, Sheffield, UK.
authors.forename: Aki
authors.initials: A
authors.lastname: Tsuchiya
authors.affiliation: Health Economics and Decision Science, School of Health and Related Research, University of Sheffield, Sheffield, UK.
authors.forename: Tracey
authors.initials: T
authors.lastname: Young
authors.affiliation: Health Economics Research Group, Brunel University, Uxbridge, UK.
authors.forename: Louise
authors.initials: L
authors.lastname: Longworth
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005060:Europe / Q000453:epidemiology; D005221:Fatigue / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D005260:Female; D006304:Health Status; D006311:Hearing Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life / Q000523:psychology; D011795:Surveys and Questionnaires / Q000592:standards*; D014786:Vision Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D055815:Young Adult
keywords: EQ-5D; bolt-on; health state valuation; hearing; tiredness; vision