Asthma is an exceedingly common chronic disease that takes a serious toll on those who suffer from it. Quality of life (QOL) is a key index of asthma's effect on individuals, and improvement in QOL is a key goal of asthma treatment (NHLBI, 2007). However, existent measures of asthma-specific QOL are conceptually limited in that they tend to confound asthma control with QOL, and may not provide valid assessments of all the key domains that are important to asthma patients. Furthermore, they are methodologically limited in that they do not take advantage of recent advances in test development that enable measures to more reliably cover the full impact of asthma on QOL experienced across the entire range of asthma severity. Limitations to existent measures have been acknowledged by leaders in the field of asthma research and practice. At the Asthma Outcomes Workshop recently convened by the National Heart, Lung, and Blood Institute of the National Institute of Health in March 2010, the Asthma Related Quality of Life Subcommittee declined to recommend any existing standard outcome instrument for measuring asthma-specific QOL. The subcommittee instead strongly recommended that new instruments be developed that measure more comprehensively the impact of asthma on QOL as a construct distinct from asthma control. The current study aims to address these limitations by developing a more precise and comprehensive model of asthma-specific QOL;constructing, testing, and validating a set of item banks for persons ages 18 and older including items from expanded QOL domains;and using Item Response Theory (IRT) analyses, creating both computer-adaptive tests and short-form measures of asthma-specific QOL. Specifically, we will: 1) develop item banks of asthma-specific QOL items, including new items developed from patient focus groups, existent QOL items from a literature review of outcome measures for asthma, and recommendations from experts on asthma, 2) evaluate the measurement properties of the item banks using field test data from a representative sample of persons aged 18+ with asthma, 3) provide preliminary information about the validity of the QOL items through associations among QOL domains identified in Aims 1 &2, analysis of mean differences in QOL by respondent characteristics, and associations between QOL domains, other selected generic QOL measures and measures of asthma control (symptoms and functional status). The use of IRT and item banking will allow for a variety of administration options, including computer based assessment, computer adaptive testing, and tailored paper and pencil short forms, all of which will minimize respondent burden and yield highly reliable and precise measurement. The measures derived from these banks can be used to monitor QOL in patients with asthma, and in clinical trials to compare the efficacy and effectiveness of different treatments. We will make the item banks and short forms available to the broader research community by posting them on a project website.
The proposed research seeks to move assessment of asthma-specific QOL forward toward measurement that is more precise, comprehensive, and flexible and seeks to use innovative methodological techniques in doing so. The development of computer-adaptive tests and short forms from asthma-specific QOL item banks will be particularly useful for monitoring QOL in patients with asthma, and for use in clinical trials to compare the efficacy and effectiveness of different treatments. Furthermore, using these item pools, future research will be better able to clarify relationships between asthma control, impairments, and asthma-specific QOL.
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