Establishment of the Minimal Clinically Important Difference (MCID) for the Ankylosing Spondylitis Quality of Life (ASQoL) Scale

OBJECTIVES: The concept of Minimal Clinically Important Difference (MCID) is crucial for meaningful interpretation of changes in patient-reported outcome measures, such as the Ankylosing Spondylitis Quality of Life (ASQoL) scale, in rheumatology. This study aimed to establish the MCID for the ASQoL scale using various methodological approaches, using real-world data from Royal Bath Hospital in the UK.

METHODS: The MCID was determined using three distribution-based methods and three anchor-based methods. Distribution-based methods included effect size, standard error of measurement (SEM), and change in standard deviation (SD). Anchor-based methods involved Change Difference, ROC curve analysis, and regression analysis. Data were analysed using these established statistical techniques. The final MCID was obtained by averaging results from all implemented methods.

RESULTS: MCID thresholds derived from different methodological approaches ranged from 0.246 to 0.869 logits. Anchor-based methods exhibited lower variability, with values between 0.284 and 0.603 logits for improvement and 0.026 to 0.577 logits for deterioration. Pragmatically averaging MCID values from different approaches yielded converging values of 0.49 logits for improvement and 0.45 logits for deterioration, suggesting a robust MCID of 0.50 logits for the ASQoL scale.

CONCLUSIONS: Establishing the MCID at 0.50 logits for the ASQoL scale represents a significant advancement in outcome measurement in rheumatology. This clinically meaningful threshold facilitates precise interpretation of changes in health-related quality of life, guiding treatment decisions and improving patient care. Future research and collaboration are needed to validate and implement this MCID across diverse patient populations, ensuring its widespread adoption in clinical practice.