Relationship between quality of life and clinical status in asthma: a factor analysis

Abstract

Many studies have shown that correlation between clinical asthma status and asthma-specific quality of life is only weak to moderate. However, this relationship has never been explored to determine whether the weakness is due to noise of measurement or whether quality of life is a distinct component of asthma health status.With a database from three clinical trials (n=763), factor analysis was used to explore the relationships between quality of life, measured by the Asthma Quality of Life Questionnaire (AQLQ), and conventional measures of asthma clinical status (symptoms, airway calibre and rescue b 2 -agonist use).The analysis revealed that although patients with severe, poorly controlled asthma tend to have worse quality of life than milder, well-controlled patients, overall asthma health status has four components (factors): asthma-specific quality of life; airway calibre; daytime symptoms and daytime b 2 -agonist use, and night-time symptoms and night-time b 2 -agonist use.The clean loading of all 21 outcomes onto four distinct and clinically identifiable factors suggests that, although some weakness of correlation between clinical indices and quality of life may be due to noise of measurement, it is mainly attributable to asthma health status being composed of distinct components. Identifying and treating impaired health-related quality of life is now recognised as an important component of asthma management. International guidelines identify that treatments should not only improve asthma clinical status, and thus reduce the risk of exacerbations and possibly airway remodelling, but should also enable patients to feel and function better in their day-to-day lives [1]. Asthma-specific quality of life questionnaires have been developed and validated so that this aspect of patient management can be accurately measured and treatment effectiveness assessed [2][3][4]. These questionnaires are now used in both clinical trials [5] and clinical practice [6] alongside the more traditional clinical measures of airway status such as airway calibre, symptoms and markers of inflammation.The rationale for including both clinical and quality of life measures has been based on the observation that correlations between these two measures are only weak to moderate and therefore patient experiences cannot be imputed from the clinical variables [2][3][4][7][8][9]. Correlations between symptoms and asthma-specific quality of life rarely exceed a Pearson correlation coefficient of 0.6 [2][3][4][7][8][9], and correlations between quality of life and airway calibre are usuallyv0.2 and rarely statistically significant [2,3,[7][8][9]. Despite the consistency of these observations [2][3][4][7][8][9], it has been argued that these poor correlations arise through imprecision of measurement (both of clinical status and of quality of life).To determine whether the weakness of association is solely attributable to noise of measurement or whether quality of life is a distinct component of asthma health status, a factor analysis w...

Quality of Life and Health Outcomes in Overweight and Non-Overweight Children With Asthma

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