Generic measures of health‐related quality of life in ankylosing spondylitis: reliability, validity and responsiveness

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