Validation of PROMIS in Diverse Populations/Clinical Study: Measuring Change in Fatigue

Evaluate how well three different patient-reported outcomes (PROs) measure individual change. 214 patients (from two sites) initiating first or new chemotherapy for any stage of breast or gastrointestinal cancer participated. The 13-item FACIT–Fatigue scale, a 7-item PROMIS® Fatigue Short-Form (PROMIS 7a), and the PROMIS® Fatigue computer adaptive test (CAT) were administered monthly online for six months. Reliability of measured change was defined, under a population mixed effects model, as the ratio of estimated systematic variance in rate-of-change to the estimated total variance of measured individual differences in rate-of-change. Precision of individual measured change, the standard error of measurement (SEM) of change, was given by the square root of the rate-of-change sampling variance. Linear and quadratic models were examined up to 3 and up to 6 months. A linear model for the reliability of measured change showed the following by 6 and by 3 months, respectively: PROMIS CAT (0.363 and 0.342); PROMIS SF (0.408 and 0.533); FACIT (0.459 and 0.473). Quadratic models offered no noteworthy improvement over linear models. Both reliability and precision results demonstrate the need to improve the measurement of intra-individual change. These results illustrate the challenge of reliably measuring individual change in fatigue with a level of confidence required for intervention. Optimizing clinically useful measurement of intra-individual differences over time continues to pose a challenge for PROs.