ABSTRACTTHE ASTHMA SYMPTOM UTILITY INDEX: RELIABILITY, VALIDITY, AND RESPONSIVENESS AMONG ADULT ASTHMA PATIENTSByChristian BimePatient reported outcome (PRO) instruments are frequently used to assess effectiveness of asthma therapy in clinical research and clinical practice. Several instruments exist for assessing asthma control and asthma-related quality of life. We used the Asthma Symptom Utility Index (ASUI), an instrument designed to assess asthma symptoms, as an example to demonstrate the methodology for evaluating the psychometric properties of PRO instruments. The ASUI is a 10-item instrument developed to measure the frequency and impact of asthma symptoms over a two week recall period. In two groups of adult asthma patients participating in large multicenter randomized trials, we showed that the ASUI has good construct validity as demonstrated by significant correlations between ASUI scores and Asthma Control Questionnaire (ACQ) scores (Spearman correlation r = -0.79, 95% CI [-0.85, -0.75], P<0.001) and Mini Asthma Quality of Life Questionnaire (Mini AQLQ) scores (r = 0.59, 95% CI [0.51, 0.61], P<0.001). The ASUI also showed robust internal consistency reliability of 0.74 (Cronbach's alpha), test-retest reliability 0.76 (intra-class correlation), as well as responsiveness to change.
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