title: Are patient-reported outcome instruments for ankylosing spondylitis fit for purpose for the axial spondyloarthritis patient? A qualitative and psychometric analysis.
abstract: OBJECTIVE
  Several patient-reported outcome (PRO) instruments have been validated in AS. This study aims to evaluate several measurement properties of such PROs in a broad axial SpA (axSpA) population, including both AS and non-radiographic axSpA (nr-axSpA) subpopulations.
  
  
  METHODS
  PROs assessed were total and nocturnal back pain, patient global assessment of disease activity, BASDAI, BASFI and the 36-item Short Form Health Survey. A literature review and both clinician and patient qualitative interviews provided information on instrument content validity. Reliability (test-retest and internal consistency), construct validity (PROs, clinical-outcome correlations and known-groups validity) and PRO responsiveness were assessed. Data from the RAPID-axSpA trial (NCT01087762) investigating certolizumab pegol efficacy in axSpA, including relevant subpopulations, were utilized.
  
  
  RESULTS
  Concepts identified for the broad axSpA population by both clinician and patient interviews were consistent with those identified through literature review of AS. All PROs demonstrated reliability in the RAPID-axSpA population (n = 325), with test-retest intraclass correlation coefficients and internal consistency Cronbach's α >0.8. Validity was supported by agreement between PROs and clinician-rated measures; except for the 36-item Short Form Health Survey Mental Components Summary, correlations between PROs and physician global assessment of disease activity ranged from 0.28 to 0.42 for week 0 and from 0.53 to 0.65 for week 24. PRO measures showed good sensitivity to change (effect size >0.8) at weeks 12 and 24 for responders. No variations in measurement properties were noted between the subpopulations.
  
  
  CONCLUSIONS
  This study indicates that both content validity and measurement properties of PRO instruments utilized in AS are preserved in the broad axSpA population.
authors.affiliation: Department of Medicine, Division of Rheumatology, Maastricht University Medical Center, Maastricht, The Netherlands, a.van.tubergen@mumc.nl.
authors.forename: Astrid
authors.initials: A
authors.lastname: van Tubergen
authors.affiliation: Clinical Outcome Assessments Consulting, ERT, Philadelphia, PA, USA and.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Black
authors.affiliation: Global Health Outcomes Research, UCB Pharma, Brussels, Belgium.
authors.forename: Geoffroy
authors.initials: G
authors.lastname: Coteur
mesh_terms: D000328:Adult; D001368:Axis, Cervical Vertebra; D003142:Communication; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D063868:Patient Outcome Assessment; D010817:Physician-Patient Relations; D011594:Psychometrics; D015203:Reproducibility of Results; D057566:Self Report; D025241:Spondylarthritis / Q000523:psychology* / Q000628:therapy; D013167:Spondylitis, Ankylosing / Q000523:psychology* / Q000628:therapy
keywords: RAPID-axSpA; ankylosing spondylitis; anti-TNF therapy; axial spondyloarthritis; certolizumab pegol; non-radiographic axSpA; patient-reported outcomes; validation