OBJECTIVE: Minimal Clinically Important Differences (MCIDs) are used as fixed numbers in the interpretation of clinical trials. Little is known about its dynamics. This study aims to explore the impact of baseline score, study setting and patient characteristics on health status MCIDs in Chronic Obstructive Pulmonary Disease (COPD).
STUDY DESIGN AND SETTING: Baseline and follow-up data on the COPD Assessment Test (CAT), Clinical COPD Questionnaire (CCQ) and St. George's Respiratory Questionnaire (SGRQ) were retrospectively analysed from Pulmonary Rehabilitation (PR) and Routine Clinical Practice (RCP). Anchor- and distribution-based MCID estimates were calculated, and tested between settings, gender, age, GOLD classification, co-morbidities and baseline health status.
RESULTS: In total, 658 patients were included with 2299 change measurements. MCID estimates for improvement and deterioration ranged for all subgroups 0.50-6.30 (CAT); 0.10-0.84 (CCQ); 0.33-12.86 (SGRQ). Larger MCID estimates for improvement and smaller ones for deterioration were noted in patients with worse baseline health status, females, elderly, GOLD I/II patients, and patients with less co-morbidities. Estimates from PR were larger.
CONCLUSION: Baseline health status and setting affected MCID estimates of COPD health status questionnaires. Patterns were observed for gender, age, spirometry classification and co-morbidity levels. These outcomes would advocate the need for tailored MCIDs.