Abstract
BackgroundThe Minimal Clinically Important Difference (MCID) assesses clinically relevant change. Its estimate might depend on the time period of measurement due to recall bias.AimThis study aimed to investigate the MCID of the Clinical COPD Questionnaire (CCQ), COPD Assessment Test (CAT) and St. George's Respiratory Questionnaire (SGRQ) using Global Ratings of Change (GRC) during different time windows.MethodsHealth status scores were collected during the RIMTCORE trial in a Pulmonary Rehabilitation (PR) setting. CCQ, CAT and SGRQ were administered at baseline, discharge, and 3/6/9/12 months. A 15-point Global Rating of Change (GRC) was administered at follow-up. The MCID was calculated as the mean change score of patients indicating a minimal change on the GRC (±2 and ±3).ResultsIn total 451 COPD patients were included for analysis (mean age 58yr, 65% male, GOLD II 50%, III 39%, IV 11%). Baseline health status scores were 2.86±1.17 (CCQ), 20.23±7.33 (CAT) and 50.69±17.33 (SGRQ). Results from the GRC analysis are presented in table 1.

Table 1: Results Global Ratings of Change
 CCQCATSGRQ
 ImprovedDeteri- oratedImprovedDeteri- oratedImprovedDeteri- orated
3 weeks-0.56 (n=196)--3.12--8.40-
3 months-0.44 (n=107)+0.42 (n=36)-2.74+2.71-7.58+5.01
6 months-0.42 (n=96)+0.48 (n=42)-2.73+3.21-9.20+5.14
9 months-0.46 (n=80)+0.50 (n=37)-2.30+3.65-10.28+6.58
12 months-0.50 (n=88)+0.66 (n=43)-2.80+4.21-8.82+7.52
 
ConclusionThe use of a 15-point GRC during various follow-up periods resulted in rather stable MCID estimates for CCQ, CAT and SGRQ. Recall bias seems of little influence on the MCID of these health status tools.