Original articleIntraindividual change in SF-36 in ambulatory clinic primary care patients predicted mortality and hospitalizations
Introduction
Health-related quality of life (HRQoL) is an important outcome in the assessment of interventions in the study of chronic diseases [1]. In addition, patient-centered HRQoL measures are used as global assessments of functional status and overall perceptions of health [2], and have been proposed as measures of disease severity. For example, the SF-36 predicts mortality in patients following coronary artery bypass graft surgery [3], successful treatment of chronic low back pain [4], and postdischarge medical services [5]. The SF-36 also has been used to predict 1-year total health plan expenses in a health maintenance organization [6], [7]. We have found that the component summary scores of the SF-36 also can be used to predict mortality in a large cohort of patients enrolled in primary care clinics [8].
For many individuals, however, HRQoL changes over time. These observed changes may reflect a true change in the HRQoL of an individual, or may result from random measurement error due to lack of precision in the instrument [9], [10], [11]. One approach to identify meaningful change has been to use the standard error of the measurement (SEM) [9], a distributional method that has the theoretical advantage of being sample independent [12]. Using the SEM criterion to define significant change, 31–64% of disadvantaged older adults had a change in one of the eight SF-36 subscales over a 12-month period [13].
Because a significant number of patients experience a change in HRQoL, we hypothesized that intraindividual change in HRQoL over time would be a better predictor of mortality and hospitalizations than a single observation. Specifically, we sought to determine whether a decrease in SF-36 scores over 1 year provides information about the risk of mortality and hospitalizations above and beyond that conveyed by a measure at one point in time using data obtained from the Ambulatory Care Quality Improvement Project (ACQUIP).
Section snippets
Subjects and setting
ACQUIP was a multicenter, randomized trial of patients receiving primary care in General Internal Medicine Clinics at seven Department of Veterans Affairs (VA) medical centers (Birmingham, AB; Little Rock, AR; San Francisco, CA; West Los Angeles, CA; White River Junction, VT; Richmond, VA; Seattle, WA) [14]. As part of this study, patients were asked to provide regular assessments of their health and satisfaction with care. This information was linked to the Veterans' Health Information System
Results
Among subjects who were sent the first SF-36, those who returned the questionnaire, compared to those that did not, were older (mean age 64.6 vs. 62.2 years), more likely to be Caucasian (78.8 vs. 68.0%), married (61.0 vs. 54.8%), not working (80.0 vs. 77.7%), and to have an annual income >$10,000 (70.8 vs. 68.5%).
Furthermore, patients who returned both the first and second SF-36 questionnaires, compared to those who returned only the first, were also older (mean age 65.4 vs. 62.7 years), more
Discussion
In this large, clinic-based study, change in SF-36, summarized in the PCS and MCS scores, was associated with both mortality and hospitalizations. We found that for many outpatients, HRQoL changed over a 1-year period, and that the direction and magnitude of intraindividual changes in measured health status provided information about the likelihood of future adverse events above and beyond that provided by a measurement at a single point in time. The relationship between change in SF-36 and
Acknowledgements
The research reported here was supported by the Department of Veteran Affairs, Health Services Research, and Development Service Grants SDR 96-002 and IIR 99-376. The views expressed in this article are those of the authors and do not necessarily represent the views of the department of Veterans Affairs.
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