BACKGROUND: Chronic obstructive pulmonary disease (COPD) is a common disease with considerable consequences for patients' daily lives. The Clinical COPD Questionnaire (CCQ) was designed to measure these consequences in daily practice. Although the CCQ is widely used, its original structure has never been tested.
AIMS: This study examines the psychometric properties of the CCQ with regard to its latent structure in a sample of primary care patients with COPD.
METHODS: Two cross-sectional studies were conducted; in study 1 (N=243) exploratory analyses, including exploratory factor analysis (EFA) and Mokken scale analysis, were performed to explore the latent structure of the CCQ. In study 2 (N=244), confirmatory factor analysis (CFA) was conducted to evaluate the model fit of the structure found in study 1.
RESULTS: Both EFA and Mokken scale analysis revealed a structure of two dimensions ('general impact' α=0.91 and 'cough' α=0.84). This structure, however, was not confirmed in study 2, nor was the original structure. However, subsequently removing items that violated the assumption of a normal response distribution did result in an excellent model fit with two dimensions measuring 'dyspnoea' and 'cough' (CFA: comparative fit index (CFI) 0.98; normed fit index (NFI) 0.97; root mean squared error of approximation (RMSEA) 0.08 (0.04)).
CONCLUSIONS: In primary care, factor analyses on the CCQ revealed a two-component structure measuring 'general impact', and 'cough'. A shortened and more specific version of the CCQ could be regarded as a useful instrument to screen for exacerbations by measuring dyspnoea, coughing and producing phlegm.