Abstract
BACKGROUND: This study compares classical test theory and item response theory frameworks to determine reliable change. Reliable change followed by anchoring to the change in categorically distinct responses on a criterion measure is a useful method to detect meaningful change on a target measure. METHODS: Adult cancer patients were recruited from five cancer centers. Baseline and follow-up assessments at 6 weeks were administered. We investigated short forms derived from PROMIS® item banks on anxiety, depression, fatigue, pain intensity, pain interference, and sleep disturbance. We detected reliable change using reliable change index (RCI). We derived the T-scores corresponding to the RCI calculated under IRT and CTT frameworks using PROMIS® short forms. For changes that were reliable, meaningful change was identified using patient-reported change in PRO-CTCAE by at least one level. For both CTT and IRT approaches, we applied one-sided tests to detect reliable improvement or worsening using RCI. We compared the percentages of patients with reliable change and reliable/meaningful change. RESULTS: The amount of change in T score corresponding to RCI(CTT) of 1.65 ranged from 5.1 to 9.2 depending on domains. The amount of change corresponding to RCI(IRT) of 1.65 varied across the score range, and the minimum change ranged from 3.0 to 8.2 depending on domains. Across domains, the RCI(CTT) and RCI(IRT) classified 80% to 98% of the patients consistently. When there was disagreement, the RCI(IRT) tended to identify more patients as having reliably changed compared to RCI(CTT) if scores at both timepoints were in the range of 43 to 78 in anxiety, 45 to 70 in depression, 38 to 80 in fatigue, 35 to 78 in sleep disturbance, and 48 to 74 in pain interference, due to smaller standard errors in these ranges using the IRT method. The CTT method found more changes compared to IRT for the pain intensity domain that was shorter in length. Using RCI(CTT), 22% to 66% had reliable change in either direction depending on domains, and among these patients, 62% to 83% had meaningful change. Using RCI(IRT), 37% to 68% had reliable change in either direction, and among these patients, 62% to 81% had meaningful change. CONCLUSION: Applying the two-step criteria demonstrated in this study, we determined how much change is needed to declare reliable change at different levels of baseline scores. We offer reference values for percentage of patients who meaningfully change for investigators using the PROMIS instruments in oncology.