Linking clinical relevance and statistical significance in evaluating intra-individual changes in health-related quality of life

OBJECTIVE. TO compare the standard error of measurement (SEM) with established standards for clinically relevant intra-individual change in an evaluation of health-related quality of life. DESIGN. Secondary analysis of data from a randomized controlled trial. SUBJECTS. Six hundred and five outpatients with a history of cardiac problems attending the general medicine clinics of a major academic medical center. MEASURES. Baseline and follow-up interviews included a modified version of the Chronic Heart Failure Questionnaire (CHQ) and the SF-36. The SEM values corresponding to established standards for minimal clinically important differences (MCIDs) on the CHQ were determined. Individual change on the SF-36 was explored using the same SEM criterion. RESULTS. One-SEM changes in this population corresponded well to the patient-driven MCID standards on all CHQ dimensions (weighted kappas (0.87; P < 0.001). The distributions of outpatients who improved, remained stable, or declined (defined by the one-SEM criterion) were generally consistent between CHQ dimensions and SF-36 subscales. CONCLUSIONS. The use of the SEM to evaluate individual patient change should be explored among other health-related quality of life instruments with established standards for clinically relevant differences. Only then can it be determined whether the one-SEM criterion can be consistently applied as a proxy for clinically meaningful change.