Abstract
The minimal clinically important difference (MCID) defines to what extent change on a health status instrument is clinically relevant, which aids scientists and physicians in measuring therapy effects. This is the first study that aimed to establish the MCID of the Clinical chronic obstructive pulmonary disease (COPD) Questionnaire (CCQ), the COPD Assessment Test (CAT) and the St George’s Respiratory Questionnaire (SGRQ) in the same pulmonary rehabilitation population using multiple approaches. In total, 451 COPD patients participated in a 3-week Pulmonary Rehabilitation (PR) programme (58 years, 65% male, 43 pack-years, GOLD stage II/III/IV 50/39/11%). Techniques used to assess the MCID were anchor-based approaches, including patient-referencing, criterion-referencing and questionnaire-referencing, and the distribution-based methods standard error of measurement (SEM), 1.96SEM and half standard deviation (0.5s.d.). Patient- and criterion-referencing led to MCID estimates of 0.56 and 0.62 (CCQ); 3.12 and 2.96 (CAT); and 8.40 and 9.28 (SGRQ). Questionnaire-referencing suggested MCID ranges of 0.28–0.61 (CCQ), 1.46–3.08 (CAT) and 6.86–9.47 (SGRQ). The SEM, 1.96SEM and 0.5s.d. were 0.29, 0.56 and 0.46 (CCQ); 3.28, 6.43 and 2.80 (CAT); 5.20, 10.19 and 6.06 (SGRQ). Pooled estimates were 0.52 (CCQ), 3.29 (CAT) and 7.91 (SGRQ) for improvement. MCID estimates differed depending on the method used. Pooled estimates suggest clinically relevant improvements needing to exceed 0.40 on the CCQ, 3.00 on the CAT and 7.00 on the SGRQ for moderate to very severe COPD patients. The MCIDs of the CAT and SGRQ in the literature might be too low, leading to overestimation of treatment effects for patients with COPD.
Highlights
Chronic obstructive pulmonary disease (COPD) is the third leading cause of death.[1]
Clinical COPD Questionnaire (CCQ), COPD Assessment Test (CAT) and St. George’s Respiratory Questionnaire (SGRQ) were normally distributed at T0 and T1; change scores were normally distributed for CCQ, CAT and SGRQ symptom scores
Our study demonstrated that the existing minimal clinically important difference (MCID) of the SGRQ and possibly of the CAT are set too low in current practice
Summary
Chronic obstructive pulmonary disease (COPD) is the third leading cause of death.[1] Spirometry is required to make the diagnosis.[2] Its parameter forced expiratory volume in 1 s (FEV1) has, a weak correlation with symptoms and disease impact, which are factors captured by health status instruments.[3] Health status has become an important goal in the management of COPD.[2] Multiple instruments exist that measure health status with the Clinical COPD Questionnaire (CCQ), COPD Assessment Test (CAT) and St. George’s Respiratory Questionnaire (SGRQ) most frequently used.[4,5,6] These tools are important in assessing treatment effectiveness. Clinically relevant change as an outcome of the questionnaires has become pivotal. The minimal clinically important difference (MCID) is a parameter that assesses clinically relevant change. It is defined as ‘the smallest difference in score, which patients perceive as beneficial and which would mandate a change in the patient’s management’.7
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