An evaluation of an asthma quality of life questionnaire as a measure of change in adults with asthma

Abstract

In assessing the effectiveness of management strategies for patients with asthma, it is important to measure outcomes which are relevant to the concerns of patients. Quality of life is one such outcome which may not be adequately reflected in lung function measurements. We have developed an asthma quality of life questionnaire (the AQLQ) for this purpose. The aim of this study was to test the validity and responsiveness of the AQLQ as a measure of change. Forty four adults with asthma were assessed on two occasions 4 months apart. On each occasion subjects completed the AQLQ and the Sickness Impact Profile (SIP). Lung function and the degree of bronchial hyperresponsiveness (BHR) were measured and diary cards were used to derive a symptom score and mean daily peak flow variability. The relation of change in AQLQ scores to change in the other outcomes was assessed. Questionnaire responsiveness was assessed by comparing the change in AQLQ scores between 19 improved and 20 stable subjects. Improvement was assessed on lung function and BHR criteria. As expected, change in AQLQ score was correlated with change in symptom score (r = 0.37, 95% CI −0.04 to 0.64) and change in BHR (r = 0.38, 95% CI 0.06 to 0.64). The associations with change in peak flow variability (r = 0.12, 95% CI −0.26 to 0.47) and change in SIP score (r = 0.18, 95% CI −0.12 to 0.45) were in the expected direction but weaker than expected. The AQLQ was capable of detecting differences between improved and stable subjects (p = 0.007). These data, in the context of the known content validity of the AQLQ, support the continued use of the AQLQ as a measure of change in adults with asthma. Further evaluation of construct validity should be incorporated into the design of clinical trials which use the AQLQ as an outcome measure.