Performance of the Asthma Impact on Quality of Life Scale (A-IQOLS) in diverse asthma research populations and demographic subgroups.

Abstract

The Asthma Impact on Quality of Life Scale (A-IQOLS) assesses the patient-perceived negative effect of asthma on quality of life. Its standard error of measurement is known; it has strong construct, convergent, and divergent validity; and it provides information that is unique among asthma outcome measures. We sought to characterize the psychometric properties of the A-IQOLS and its suitability for use in demographically and clinically diverse adult asthmatic populations. Data from participants in 5 independent asthma studies, with samples ranging from patients with well-controlled moderate asthma to patients with severe poorly controlled asthma, were pooled to determine the psychometric performance of A-IQOLS scores overall and in multiple demographic, disease status, and study subgroups. Pooled sample (n = 597) age averaged 45 years; 66% were female, 65% were white, 22% were African American, 11% were Hispanic, and 11% had a high school education or less. The rated importance of its underlying life dimensions and associations between A-IQOLS scores and lung function, symptom, Asthma Control Test, Juniper Mini Asthma Quality of Life Questionnaire, and Marks Asthma Quality of Life Questionnaire scores was very similar, regardless of patients' demographic and clinical characteristics. A-IQOLS scores discriminated among the individual study samples, as well as other patient-reported symptom and functional status measures. Distribution and anchor-based considerations suggest an A-IQOLS minimum clinically important difference in the vicinity of 0.50 and not less than 0.33 scale score units. A-IQOLS is valid for research and potentially clinical use in demographically and clinically diverse patients.