title: Generic measures of health-related quality of life in ankylosing spondylitis: reliability, validity and responsiveness.
abstract: OBJECTIVE
  To assess the acceptability and measurement properties of two generic measures of health-related quality of life (HRQL): the EuroQol and the Short Form 12-item Health Survey Questionnaire (SF-12) in ankylosing spondylitis (AS).
  
  
  METHODS
  Instruments were administered by means of a self-completed questionnaire to AS patients recruited from across the United Kingdom. Instruments were assessed for data quality and scaling assumptions. Test-retest reliability was assessed in those patients reporting no change in general health at 2 weeks. The convergent validity of both instruments was assessed and scores were correlated with responses to health transition questions. Responsiveness was assessed for patients reporting change in health at 6 months.
  
  
  RESULTS
  The instruments had high completion rates. Although slightly skewed towards better levels of health, scores covered the available range for both sections of the EuroQol [EQ-5D and EQ-visual analogue scale (EQ-VAS)]. Score distributions approximated normality for the SF-12. Test-retest reliability estimates support the use of both instruments in group evaluation and the SF-12 Physical Component Summary score (PCS) in individual evaluation (>0.90). Correlations between instruments were in the hypothesized direction and were of a moderate level. The EQ-VAS had the strongest linear relationship, with responses to both specific and general health transition questions (P<0.01). The EQ-VAS and SF-12 PCS were the most responsive instruments. The EQ-5D was the least responsive instrument.
  
  
  CONCLUSIONS
  The instruments have undergone a comprehensive comparative evaluation to assess the measurement properties required for patient-assessed measures of health outcome in AS. Adequate levels of acceptability, reliability and validity were found for both instruments. Although evidence supporting instrument responsiveness was strong for the EQ-VAS and SF-12 PCS, it was very weak for the EQ-5D and SF-12 Mental Component Summary Scale (MCS). The EQ-VAS and SF-12 PCS can both be recommended for use in group evaluation, and the SF-12 PCS is recommended in routine practice or research. However, the lower reliability of the SF-12 MCS and the limited ability of both the EQ-5D and SF-12 MCS to detect change in health may restrict these roles.
authors.affiliation: Department of Health Sciences and Clinical Evaluation, University of York, York YO1 5DD, UK.
authors.forename: K L
authors.initials: KL
authors.lastname: Haywood
authors.forename: A M
authors.initials: AM
authors.lastname: Garratt
authors.forename: K
authors.initials: K
authors.lastname: Dziedzic
authors.forename: P T
authors.initials: PT
authors.lastname: Dawes
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D015203:Reproducibility of Results; D013167:Spondylitis, Ankylosing / Q000523:psychology*; D011795:Surveys and Questionnaires