Validation of the Ankylosing Spondylitis Quality of Life assessment tool in patients with non-radiographic axial spondyloarthritis
Bengt Hoepken, Daniel Serrano, Kristina Harris, Mark C. Hwang, John D. Reveille
Abstract
PURPOSE: To evaluate the psychometric performance of the Ankylosing Spondylitis Quality of Life (ASQoL) scale in patients with non-radiographic axial spondyloarthritis (nr-axSpA) to assess its appropriateness as an outcome measure in future clinical studies. METHODS: Patients with active axSpA from a Phase III, randomized, double-blind, placebo-controlled trial (RAPID-axSpA, NCT01087762) were included (N = 325). Modified New York (mNY) classification criteria were used to classify patients as having ankylosing spondylitis or nr-axSpA; those with nr-axSpA were further categorized based on objective signs of inflammation. Psychometric properties of the ASQoL were assessed/documented using a mixture of modern psychometric methods and classical test theory methods. These included exploratory factor analysis and item response theory models to assess the domain structure, test the utility of a single domain relative to subdomains, assess bias, and generate statistics to guide an empirical scoring algorithm. The reliability and validity of scores were evaluated via internal consistency, test-retest reliability, concurrent validity, and known-groups validity. Score responsiveness was assessed via anchor-based clinically meaningful change, supplemented with empirical cumulative distribution function visualizations. RESULTS: The ASQoL data were defined by four domains. However, a four-domain solution was found to be inferior to a bifactor solution in which the four domains were included within a total domain. Scoring statistics supported a unit-weighted total score. Within the nr-axSpA population with objective signs of inflammation, the ASQoL mean score had adequate reliability, validity, and ability to detect clinically meaningful change. CONCLUSIONS: Our findings suggest that the ASQoL is an appropriate outcome measure in interventional clinical trials in patients with nr-axSpA.