The Ankylosing Spondylitis Quality of Life Questionnaire: validation in a New Zealand cohort

Abstract

To examine the validity of the Ankylosing Spondylitis Quality of Life Questionnaire (ASQoL) in a New Zealand population with defined axial spondyloarthritis (SpA). Once validated, the ASQoL will be included as an outcome measure in a proposed multicentre New Zealand study. Five healthy participants were interviewed to identify any issues related to local dialect or linguistic comprehension of the questionnaire. Cognitive debriefing interviews were conducted with four participants with SpA to assess the relevance and comprehensiveness of the questionnaire. Internal consistency was established by determining the Cronbach's alpha. Finally, convergent validity of the ASQoL was assessed by testing the correlation with the Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and patient global visual analogue scale (VAS) scores in a cohort of 63 SpA patients. The language used in the ASQoL was considered clear, comprehensible and accessible to speakers of New Zealand English. The questionnaire displayed content validity for patients with SpA. The ASQoL had good internal consistency in the present sample (α = 0.854). A positive correlation was found between the ASQoL and the BASFI (rho = 0.635, P < 0.001), BASDAI (rho = 0.521, P < 0.001) and patient global assessment VAS (rho = 0.546, P < 0.001), providing evidence that the ASQoL has convergent validity among patients with SpA in New Zealand. Test-retest reliability was good over 16 weeks (rho = 0.730, P < 0.001). The ASQoL has been demonstrated in this study to be feasible, internally consistent and to have content and convergent validity in a New Zealand population of patients with axial spondyloarthritis; it is a measure of quality of life which is both easy to employ and reliable.