Reliability and validity of the Asthma Quality of Life Questionnaire--marks in a sample of adult asthmatic patients in the United States.

To render quality-of-life scores on an instrument acceptable for cross-national comparison, the instrument's reliability and validity must be established in all countries in question. The Asthma Quality of Life Questionnaire-Marks (AQLQ-M) was developed in Australia, where it was shown to have good reliability and validity. However, no attempt had been made to determine the psychometric properties of the AQLQ-M and its domains (i.e., Breathlessness, Mood, Social, and Concerns) in the United States. The objectives of the present study were to administer the AQLQ-M to a sample of adult asthmatic patients in the United States (N = 106) and assess (1) the acceptability of the AQLQ-M to respondents, (2) the internal consistency of the AQLQ-M and its domains, and (3) the construct validity of the AQLQ-M and its domains. Results indicated that respondents did not have difficulty answering the questions in the AQLQ-M. The Cronbach coefficient alpha value for the AQLQ-M was 0.94. The Cronbach coefficient alpha value for individual domains ranged from 0.84 to 0.91, providing evidence of good internal consistency reliability for the AQLQ-M and its domains. Pearson product-moment correlations between the domain scores ranged from 0.62 to 0.88, indicating that the domains were related but separate aspects of asthma-specific quality of life, as measured by the AQLQ-M. Spearman rank-order correlations of the AQLQ-M score and domain scores with an indicator of disease severity--number of different prescription medications taken for asthma in the preceding 3 months-were positive and significant. This indicated that subjects taking a greater number of prescription asthma medications had higher AQLQ-M and domain scores, or a greater negative impact of asthma on quality of life, a result consistent with previous findings and one that provides some evidence of convergent validity. Our findings support the use of the AQLQ-M as a decision-making tool in the United States and in cross-national comparisons between the United States and Australia.