Sensitivity of quality of life domains and constructs to longitudinal change in a clinical trial comparing salmeterol with placebo in asthmatics

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Abstract
The quality of life (QOL) benefits of salmeterol versus placebo were compared in a double-blind, multicentre study using the Living with Asthma Questionnaire (LWAQ) which was scored in three different ways. First, the overall LWAQ score showed that salmeterol enhanced QOL compared to placebo. Second, when the LWAQ was analysed in terms of its two construct subscales we found, as predicted previously, that the Problem construct was more sensitive to longitudinal change compared with the Evaluation construct. Third, when the LWAQ was analysed in terms of its 11 domain subscales we found a significant improvement for salmeterol compared with placebo on three domains, Sport, Sleep, and Work and other activities. Analysing clinical trial results in terms of construct subscales and domain subscales provides different kinds of information each of which is useful. Analysis in terms of overall QOL scores is less informative.