Background: The World Health Organization Disability Assessment Schedule 2.0 has been used to measure postoperative disability in several clinical trials and cohort studies. It is uncertain what the minimal clinically important difference or patient-acceptable symptom state scores are for this scale in patients recovering from surgery.
Methods: The authors analyzed prospectively collected data from three studies that measured disability 3 and 6 months after surgery. Three distribution-based methods (0.3 multiplied by SD, standard error of the measurement, and 5% range) and two anchor-based methods (anchored to two patient-rated health status questions and separately to unplanned hospital readmission) were averaged to estimate the minimal clinically important difference for the World Health Organization Disability Assessment Schedule 2.0 score converted to a percentage scale. Scores consistent with a patient-acceptable symptom state and clinically significant disability were determined by an anchored 75th centile method.
Results: Data from 4,361 patients were analyzed. The average minimal clinically important difference estimate for the World Health Organization Disability Assessment Schedule 2.0 was 5%, with similar estimates in patients with or without preoperative disability. The patient-acceptable symptom state score was 16%, and the score consistent with at least moderate clinically significant disability was 35%. Using these estimates, between baseline and 6 months after surgery, 21% of patients had a significant increase in disability, and 73% achieved a patient-acceptable symptom state.
Conclusions: A change in World Health Organization Disability Assessment Schedule 2.0 score of 5% or more after surgery is consistent with a clinically important change in disability. Patients with a score less than 16% after surgery have an acceptable symptom state and can be considered as disability-free, whereas patients with a score of 35% or more can be considered as having at least moderate clinically significant disability.