Is the St. George's Respiratory Questionnaire an Appropriate Measure of Symptom Severity and Activity Limitations for Clinical Trials in COPD? Analysis of Pooled Data from Five Randomized Clinical Trials

Purpose: The objective of this study was to examine the psychometric properties of the St. George's Respiratory Questionnaire (SGRQ) in patients with chronic obstructive pulmonary disease (COPD) using Rasch measurement theory (RMT) analyses.

Materials and methods: RMT analysis was conducted on the baseline SGRQ data from five multi-national, Phase III randomized trials investigating a fixed-dose combination of a long-acting β2-agonist and a long-acting muscarinic antagonist in COPD patients. Analysis was performed for the SGRQ "Symptoms" and "Activity" domains. An exploratory analysis was also conducted using the different specific symptoms as defined in the reconceptualization of the SGRQ "Symptoms" domain. Differential item functioning (DIF) analysis was performed for geographical regions on the "Activity" domain, in order to explore cross-cultural validity of the SGRQ.

Results: Overall, the SGRQ "Activity" domain showed good measurement property, but two items ("Sitting or lying still making feel breathless" and "Playing sports or game making feel breathless") showed very high fit residuals. The SGRQ "Symptoms" domain demonstrated good targeting; however, two items showed disordered thresholds ("Coughed" and "Brought up phlegm"). In an exploratory RMT analysis, measures for "Cough and Sputum", "Breathing difficulties" or "Wheezing attacks" showed unsatisfactory measurement properties with poor reliability (person separation index = 0.35, 0.66 and 0.16, respectively) and targeting issues. The examination of cross-cultural performances of the SGRQ "Activity" items showed a great variability in the responses to these items in different global regions.

Conclusion: Our results indicated that SGRQ may not be an appropriate instrument to measure symptom severity or activity limitations in patients with COPD. Hence, there is a need to develop other relevant PRO instruments that can be used in conjunction with SGRQ to provide a holistic assessment of the health status of COPD patients in clinical research.