Psychometric sensitivity analyses can identify bias related to measurement properties in trials that use patient-reported outcome measures: a secondary analysis of a clinical trial using the disabilities of the arm, shoulder, and hand questionnaire.

OBJECTIVES: Demonstrate psychometric sensitivity analyses for testing the stability of study findings to assumptions made about patient-reported outcome measures. STUDY DESIGN AND SETTING: We performed secondary analyses of Disability of Arm, Shoulder, and Hand (DASH) data collected within the Prevention of Shoulder Problems clinical trial, which compared upper limb function scores in women who had undergone breast cancer surgery, randomized to either an exercise program or usual care. We repeated the principal trial analyses after grouping DASH items into subscales suggested by factorial analyses in this dataset and applied item response theory to account for unequal item weighting. We checked for measurement invariance by participant age and response shift bias using established techniques. RESULTS: Our analyses suggested that the DASH measured two constructs: motor function and sensory symptoms. The majority of the six-month difference in DASH score was driven by motor function. With item response theory scoring, we found differences in both constructs at 12 months (P = 0.019 and P = 0.007), but in neither construct at 6 months, contrary to the original trial results. We found no differential item function by age or between baseline and 12-month measurements. CONCLUSIONS: Psychometric sensitivity analyses aid in the interpretation of the Prevention of Shoulder Problems trial's results.