Likely change indexes improve estimates of individual change on patient-reported outcomes

Individual change on a patient-reported outcome (PRO) measure can be assessed by statistical significance and meaningfulness to patients. We explored the relationship between these two criteria by varying the confidence levels of the coefficient of repeatability (CR) on the Patient-Reported Outcomes Measurement Information System (R) Physical Function (PF) 10a (PF10a) measure.

In a sample of 1129 adult cancer patients, we estimated individual-change thresholds on the PF10a from baseline to 6 weeks later with the CR at 50%, 68%, and 95% confidence. We also assessed agreement with group- and individual-level thresholds from anchor-based methods [mean change and receiver operating characteristic (ROC) curve] using a PF-specific patient global impression of change (PGIC).

CRs at 50%, 68%, and 95% confidence were 3, 4, and 7 raw score points, respectively. The ROC- and mean-change-based thresholds for deterioration were -4 and -6; for improvement they were both 2. Kappas for agreement between anchor-based thresholds and CRs for deterioration ranged between κ = 0.65 and 1.00, while for improvement, they ranged between 0.35 and 0.83. Agreement between the PGIC and all CRs always fell below "good" (κ < 0.40) for deterioration (0.30-0.33) and were lower for improvement (0.16-0.28).

In comparison to the CR at 95% confidence, CRs at 50% and 68% confidence (considered likely change indexes) have the advantage of maximizing the proportion of patients appropriately classified as changed according to statistical significance and meaningfulness.