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 establis hed standards for clinically relevant intra-individual change in an evaluat ion 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 proble ms attending the general medicine clinics of a major academic medical cente r. 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 di fferences (MCIDs) on the CHQ were determined. Individual change on the SF-3 6 was explored using the same SEM criterion. RESULTS. One-SEM changes in this population corresponded well to the patien t-driven MCID standards on all CHQ dimensions (weighted kappas (0.87; P < 0 .001). The distributions of outpatients who improved, remained stable, or d eclined (defined by the one-SEM criterion) were generally consistent betwee n CHQ dimensions and SF-36 subscales. CONCLUSIONS. The use of the SEM to evaluate individual patient change shoul d be explored among other health-related quality of life instruments with e stablished 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.