Measuring True Change in Individual Patients: Reliable Change Indices of Cardiac Rehabilitation Outcomes, and Implications for Quality Indicators

BACKGROUND: Mediated by outcomes such as improved exercise capacity, cardiac rehabilitation (CR) reduces morbidity and mortality. For accuracy, an individual CR patient's change must be measured reliably, an issue not typically considered in practice. Drawing from psychometric theory, we calculated reliable change indices (RCIs), to measure individual CR patients’ true clinical change, apart from that from error and test practice/exposure, in exercise capacity, anxiety, and depression. METHODS: Indirectly calculated exercise capacity (peak metabolic equivalents [METs]) and psychological symptoms were each measured twice, 1 week apart, by administering treadmill tests or the Hospital Anxiety and Depression Scale (HADS) to separate samples of 35 (mean age: 59.0 years; 6 women) and 96 (mean age: 64.4 years; 32 women) CR patients, respectively. Using test-retest reliability and mean difference scores from these samples to estimate error and practice/exposure effects, we calculated RCIs for a separate cohort (n = 2066; mean age: 62.0 years; 533 women) who completed 6-month CR, and compared change distributions (worsened/unchanged/improved) based on critical RCIs, mean and percent changes, cut-off scores, and standard deviations. RESULTS: Practice/exposure effects were nonsignificant, except the mean HADS anxiety score decreased significantly (P ≤ 0.013; d = 0.17, small effect). Test-retest reliabilities were high (METs r = 0.934; HADS anxiety score r = 0.912; HADS depression score r = 0.90; P < 0.001). Among 2066 CR patients, RCI distributions differed (P < 0.001) from those of most other change criteria. CONCLUSIONS: Change ascertainment depends on criterion choice. A Canadian Cardiovascular Society CR quality indicator of increase by 0.5 MET may be too small to assess individuals’ functional capacity change. RCIs offer a pragmatic approach to benchmarking reliable change frequency, and pending further validation, could be used for feedback to individual patients.