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Validation of a standardized version of the Asthma Quality of Life Questionnaire
E F Juniper1, A S Buist, F M Cox
1Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada. juniper@fhs.mcmaster.ca
Background:
In the original 32-item Asthma Quality of Life Questionnaire (AQLQ), five activity questions are selected by patients themselves. However, for long-term studies and large clinical trials, generic activities may be more appropriate.
Methods:
For the standardized version of the AQLQ, the AQLQ(S), we formulated five generic activities (strenuous exercise, moderate exercise, work-related activities, social activities, and sleep) to replace the five patient-specific activities in the AQLQ. In a 9-week observational study, we compared the AQLQ with the AQLQ(S) and examined their measurement properties. Forty symptomatic adult asthma patients completed the AQLQ(S), the AQLQ, the Medical Outcomes Survey Short Form 36, the Asthma Control Questionnaire, and spirometry at baseline, 1, 5, and 9 weeks.
Results:
Activity domain scores (mean +/- SD) were lower with the AQLQ (5.7 +/- 0.9) than with the AQLQ(S) (5.9 +/- 0.8; p = 0.0003) and correlation between the two was moderate (r = 0.77). However, for overall scores, there was minimal difference (AQLQ, 5.4 +/- 0.8; AQLQ(S), 5.5 +/- 0.8; r = 0.99). Reliability (AQLQ intraclass correlation coefficient, 0.95; AQLQ(S) intraclass correlation coefficient, 0.96) and responsiveness (AQLQ, p < 0.0001; AQLQ(S), p < 0.0001) were similar for the two instruments. Construct validity (correlation with other measures of health status and clinical asthma) was also similar for the two instruments.
Conclusions:
The AQLQ(S) has strong measurement properties and is valid for measuring health-related quality of life in asthma. The choice of instrument should depend on the task at hand.