Reliability and validity of the clinical COPD questionniare and chronic respiratory questionnaire.
BACKGROUND
Questionnaires are often used in assessing health-related quality of life in patients with chronic obstructive pulmonary disease (COPD). It is important that these questionnaires have good reliability, validity, and responsiveness. The aim of this study was to investigate and compare these properties in the disease specific Clinical COPD Questionnaire (CCQ) and the Chronic Respiratory Questionnaire self-reported (CRQ-SR).


METHODS
Two hundred ninety six participants with spirometry confirmed mild to moderate COPD were included in a smoking cessation trial. It was assumed that health-related quality of life would improve in participants who stopped smoking. The questionnaires were administered at baseline and at weeks 5, 26, and 52 after the target quit date.


RESULTS
At baseline, 292 (97%) participants returned the CCQ and 296 (100%) the CRQ-SR questionnaire. For both instruments, the internal consistency was good (Cronbach's alpha >70%) as was the convergent validity with each other but not with spirometry. The CCQ was responsive to improvements in respiratory symptoms at both week 26 (-1.02, SD = 0.81) and 52 (-1.04, SD = 0.91) and in the total score at week 26 (-0.54, SD = 0.50) and 52 (-0.43, SD = 0.44). The mastery domain and the total score of the CRQ-SR were responsive at week 26 (1.14, SD = 0.82; 0.67, SD = 0.97 respectively) but not at week 52 (0.04, SD = 0.93; 0.38, SD = 0.57 respectively).


CONCLUSION
Both the CCQ and CRQ-SR are equally reliable and valid. The long-term responsiveness of the CCQ is better. Both questionnaires can be used in future studies involving patients with mild to moderate COPD. However, when the follow-up exceeds 26 weeks, the CCQ is the recommended alternative. Netherlands Trial Register: ISRCTN 64481813.