Original articlesGeneric and Specific Measurement of Health-Related Quality of Life in a Clinical Trial of Respiratory Rehabilitation
Introduction
The increasing recognition that we must judge therapy for chronic disease on the basis of its effects on how patients feel highlights the need for optimal measurement of patients’ experience [1]. Generic health-related quality of life (HRQL) measures provide comprehensive ratings that allow comparison across patient groups and across therapies [2]. Generic measures may, however, not perform well in measuring crucial disease-specific aspects of HRQL and in particular may fail to detect important treatment effects if their magnitude is not large [3].
Disease-specific measures provide an alternative to generic health status measures and may be more responsive to small but important changes in HRQL. Indeed, many investigators are convinced that specific measures are required to ensure responsiveness. However, there have been few head-to-head comparisons between different HRQL measurement instruments in the setting of randomized controlled trials (RCTs) and even fewer explorations of relative validity. Because a major use of HRQL instruments in the clinical arena is to determine effects of new treatments, comparisons in RCTs provide the strongest evidence regarding differential measurement properties, and examination of both responsiveness and validity would be instructive.
Chronic airflow limitation (CAL) is a long-term, disabling condition in which the best we can hope for is to ameliorate the negative impact on HRQL. Rehabilitation improves HRQL without major changes in physiologic function [4] and provides a useful setting for exploring the relative merits of alternative approaches to measurement. We recently reported [5] the results of a randomized trial demonstrating improvement in disease-specific HRQL as a result of respiratory rehabilitation. In this article, we compare the responsiveness and validity of a number of HRQL measures we administered during this study.
Section snippets
The Trial
The full methods of this study are reported elsewhere [5]. In brief, we randomized 89 patients with stable moderate or severe CAL to receive an 8-week inpatient rehabilitation program followed by gradually decreasing outpatient follow-up or conventional community care. A trained interviewer blinded to group allocation obtained measurements at baseline and reviewed patients’ progress at 12, 18, and 24 weeks after randomization. Of the 89 patients, 45 entered the rehabilitation group, and 44, the
Results
Table 1 presents the first comparison of the responsiveness of the instruments. The table includes the mean scores during control and rehabilitation periods and the associated effect sizes and P values. We include, for the sake of comparison, the 6-minute walk test. Other than the 6-minute walk, which is listed first, we present the measures in order of their power to differentiate treatment from control, the lowest P values reflecting the greatest responsiveness. The four domains of the CRQ
Discussion
Generic measures of HRQL have a major advantage over disease-specific measures in that they are applicable across conditions and thus allow comparisons of HRQL, and changes in HRQL with treatment, in patient groups. Generic measures that provide a single summary score provide information on the net change in HRQL, the treatment effect minus the side effects. Generic measures also permit comparisons of patients to population norms. Generic utility measures have a further advantage in that
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Dr. Guyatt is a Career Scientist of the Ontario Ministry of Health.