title: Measurement properties of the Health Assessment Questionnaire Disability Index for generalized osteoarthritis.
abstract: OBJECTIVE
  Generalized OA (GOA) is highly prevalent in OA. Individuals with GOA typically suffer from limitations of both upper and lower extremity function, yet we lack a validated instrument to assess their activity limitations. An appropriate instrument might be the HAQ Disability Index (HAQ-DI). Therefore the aim of this study was to evaluate the measurement properties of the HAQ-DI in GOA.
  
  
  METHODS
  Data were used from a randomized controlled trial comparing the effectiveness of two multidisciplinary treatment programmes for patients with GOA. One hundred and thirty-seven of 147 included patients completed a standardized set of questionnaires before and after treatment. Interpretability, validity, reliability and responsiveness of the HAQ-DI were assessed using the Consensus-Based Standards for the Selection of Health Status Measurement Instruments checklist (COSMIN).
  
  
  RESULTS
  Floor and ceiling effects were present. The content validity was questionable since the HAQ-DI encompasses activities that are either not relevant or too easy to perform as judged by patients and experts. Construct validity was good since 90% of the hypotheses were confirmed. Factor analysis confirmed the unidimensionality of the HAQ-DI (root mean square error of approximation = 0.057, χ(2)/df ratio = 1.48). Cronbach's α was 0.90, confirming internal consistency and the ICC was 0.81, reflecting good reliability. The minimal important change was 0.25 and the smallest detectable change was 0.60. We could not establish the responsiveness of the HAQ-DI.
  
  
  CONCLUSIONS
  The HAQ-DI showed good construct validity, internal consistency and reliability, whereas its content validity and responsiveness were limited. We recommend updating the items of the HAQ-DI in future research focusing on functional limitations in GOA.
  
  
  BACKGROUND
  Dutch Trial Register NTR2137, http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2137.
authors.affiliation: Department of Rheumatology, Sint Maartenskliniek, Nijmegen, Department of Orthopaedics, University Medical Center, Leiden and Department of Epidemiology, CAPHRI School for Public Health and Primary Care, CCTR Centre for Care Technology Research, Maastricht University, Maastricht, The Netherlands n.cuperus@maartenskliniek.nl.
authors.forename: Nienke
authors.initials: N
authors.lastname: Cuperus
authors.affiliation: Department of Rheumatology, Sint Maartenskliniek, Nijmegen, Department of Orthopaedics, University Medical Center, Leiden and Department of Epidemiology, CAPHRI School for Public Health and Primary Care, CCTR Centre for Care Technology Research, Maastricht University, Maastricht, The Netherlands.
authors.forename: Elien A M
authors.initials: EA
authors.lastname: Mahler
authors.affiliation: Department of Rheumatology, Sint Maartenskliniek, Nijmegen, Department of Orthopaedics, University Medical Center, Leiden and Department of Epidemiology, CAPHRI School for Public Health and Primary Care, CCTR Centre for Care Technology Research, Maastricht University, Maastricht, The Netherlands.
authors.forename: Theodora P M
authors.initials: TP
authors.lastname: Vliet Vlieland
authors.affiliation: Department of Rheumatology, Sint Maartenskliniek, Nijmegen, Department of Orthopaedics, University Medical Center, Leiden and Department of Epidemiology, CAPHRI School for Public Health and Primary Care, CCTR Centre for Care Technology Research, Maastricht University, Maastricht, The Netherlands.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Hoogeboom
authors.affiliation: Department of Rheumatology, Sint Maartenskliniek, Nijmegen, Department of Orthopaedics, University Medical Center, Leiden and Department of Epidemiology, CAPHRI School for Public Health and Primary Care, CCTR Centre for Care Technology Research, Maastricht University, Maastricht, The Netherlands.
authors.forename: Cornelia H
authors.initials: CH
authors.lastname: van den Ende
mesh_terms: D000368:Aged; D018501:Antirheumatic Agents / Q000627:therapeutic use; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D010003:Osteoarthritis / Q000175:diagnosis* / Q000188:drug therapy; D063868:Patient Outcome Assessment; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D016896:Treatment Outcome
chemical_list: D018501:Antirheumatic Agents
keywords: HAQ-DI; activity limitations; functional limitations; generalized osteoarthritis; measurement properties