Composite outcomes, in which multiple end points are combined, are frequently
used as primary outcome measures in randomized trials and are often associated
with increased statistical efficiency. However, such measures may prove challenging
for the interpretation of results. In this article, we examine the use of
composite outcomes in major clinical trials, assess the arguments for and
against them, and provide guidance on their application and reporting. To
assess incidence and quality of reporting, we systematically reviewed the
use of composite end points in clinical trials in Annals
of Internal Medicine, BMJ, Circulation, Clinical Infectious Diseases, Journal of the American College of Cardiology, JAMA, Lancet, New England
Journal of Medicine, and Stroke from 1997
through 2001 using a sensitive search strategy. We selected for review 167
original reports of randomized trials (with a total of 300 276 patients)
that included a composite primary outcome that incorporated all-cause mortality.
Sixty-three trials (38%) were neutral both for the primary end point and the
mortality component. Sixty trials (36%) reported significant results for the
primary outcome measure but not for the mortality component. Only 6 trials
(4%) were significant for the mortality component but not for the primary
composite outcome, whereas 19 trials (11%) were significant for both. Twenty-two
trials (13%) were inadequately reported. Our review suggests that reporting
of composite outcomes is generally inadequate, implying that the results apply
to the individual components of the composite outcome rather than only to
the overall composite. Current guidelines for the undertaking and reporting
of clinical trials could be revised to reflect the common use of composite
outcomes in clinical trials.
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