bias due to changes in specified outcomes during the systematic review process偏差变化引起系统审查过程中指定的结果.pdf
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Bias Due to Changes in Specified Outcomes during the
Systematic Review Process
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Jamie J. Kirkham *, Doug G. Altman , Paula R. Williamson
1 Centre for Medical Statistics and Health Evaluation, University of Liverpool, Liverpool, England, 2 Centre for Statistics in Medicine, University of Oxford, Oxford, England
Abstract
Background: Adding, omitting or changing outcomes after a systematic review protocol is published can result in bias
because it increases the potential for unacknowledged or post hoc revisions of the planned analyses. The main objective of
this study was to look for discrepancies between primary outcomes listed in protocols and in the subsequent completed
reviews published on the Cochrane Library. A secondary objective was to quantify the risk of bias in a set of meta-analyses
where discrepancies between outcome specifications in protocols and reviews were found.
Methods and Findings: New reviews from three consecutive issues of the Cochrane Library were assessed. For each review,
the primary outcome(s) listed in the review protocol and the review itself were identified and review authors were
contacted to provide reasons for any discrepancies. Over a fifth (64/288, 22%) of protocol/review pairings were found to
contain a discrepancy in at least one outcome measure, of which 48 (75%) were attributable to changes in the primary
outcome measure. Where lead authors could recall a reason for the discrepancy in the primary outcome, there was found to
be potential bias in nearly a third (8/28, 29%) of these reviews, with changes being made after knowledge of the results
from individual trials. Only 4(6%) of the 64 reviews with an outcome discrepancy described the reason for the change in the
review, with no acknowledgment of the change in any o
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