An empirical comparison of the St George's Respiratory Questionnaire (SGRQ) and the Chronic Respiratory Disease Questionnaire (CRQ) in a clinical trial setting

Abstract

Background: The Chronic Respiratory Questionnaire (CRQ) and the St George's Respiratory Questionnaire (SGRQ) are the two most widely used quality of life questionnaires in chronic obstructive pulmonary disease (COPD). A study was undertaken to compare directly the self-administered version of the CRQ and the SGRQ with respect to feasibility, internal consistency, validity, and sensitivity to changes resulting from bronchodilator therapy.

Methods: One hundred and forty four patients with moderate or severe COPD were randomly assigned to receive three months of treatment with either salmeterol, salmeterol + ipratropium bromide, or placebo. Quality of life was measured at baseline and after 12 weeks of treatment.

Results: The proportions of missing values per patient were low for both questionnaires (0.54% for the CRQ and 2% for the SGRQ). The internal consistency was good for both questionnaires (Cronbach's alpha coefficients >/= 0.84 for the CRQ and >/= 0.76 for the SGRQ). Factor analysis confirmed the original domain structure of the CRQ but not of the SGRQ. Correlations with forced expiratory volume in one second (FEV(1)) % predicted and peak expiratory flow rate (PEFR) were low for both questionnaires but better for the SGRQ than for the CRQ. The ability to discriminate between subjects with different levels of FEV(1) was somewhat better for the SGRQ. The correlations with symptom scores were comparable for both questionnaires. Cross sectionally, the scores of the two questionnaires were moderately to highly correlated (coefficients ranged from 0.35 to 0.72). Longitudinally, these correlations were lower (coefficients ranged from 0.17 to 0.54) but were still significant. The CRQ total and emotions score and the SGRQ symptoms score were the most responsive to change. The SGRQ symptoms domain was the only domain where the improvement in patients receiving combination treatment crossed the threshold for clinical relevance.

Conclusions: Since this analysis of reliability, validity, and responsiveness to change did not clearly favour one instrument above the other, the choice between the CRQ and the SGRQ can be based on other considerations such as the required sample size or the availability of reference values.