The psychometric properties and minimal clinically important difference for disability assessment using WHODAS 2.0 in critically ill patients

Objectives: The 12-item World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0) provides a standardised method for measuring health and disability. This study aimed to determine its reliability, validity and responsiveness and to establish the minimum clinically important difference (MCID) in critically ill patients. Design: Prospective, multicentre cohort study. Setting: Intensive care units of six metropolitan hospitals. Participants: Adults mechanically ventilated for > 24 hours. Main outcome measures: Reliability was assessed by measuring internal consistency. Construct validity was assessed by comparing WHODAS 2.0 scores at 6 months with the EuroQoL visual analogue scale (EQ VAS) and Lawton Instrumental Activities of Daily Living (IADL) scale scores. Responsiveness was evaluated by assessing change over time, effect sizes, and percentage of patients showing no change. The MCID was calculated using both anchor and distribution-based methods with triangulation of results. Main results: A baseline and 6-month WHODAS 2.0 score were available for 448 patients. The WHODAS 2.0 demonstrated good correlation between items with no evidence of item redundancy. Cronbach α coefficient was 0.91 and average split-half coefficient was 0.91. There was a moderate correlation between the WHODAS 2.0 and the EQ VAS scores (r = -0.72; P < 0.001) and between the WHODAS 2.0 and the Lawton IADL scores (r = -0.66; P < 0.001) at 6 months. The effect sizes for change in the WHODAS 2.0 score from baseline to 3 months and from 3 to 6 months were low. Ceiling effects were not present and floor effects were present at baseline only. The final MCID estimate was 10%. Conclusion: The 12-item WHODAS 2.0 is a reliable, valid and responsive measure of disability in critically ill patients. A change in the total WHODAS 2.0 score of 10% represents the MCID.