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Abstract
ObjectivesTo determine the incidence of outcome switching in follow-up publications of randomized controlled trials. Outcome switching leads to bias where treatment benefits are more likely to be overestimated or based on chance. Study design and settingMeta-research study including all follow-up publications 2014-2018 in the New England Journal of Medicine, The Lancet, the Journal of the American Medical Association, and the British Medical Journal. Two independent reviewers compared the primary outcomes of follow-up publications with the original RCT publication and the trial protocol. ResultsSeventy-eight follow-up publications were identified. Thirty-one (40%) used different primary outcomes in the follow-up publication compared with the original RCT. In seventeen (55%) of these the outcome switch was neither pre-specified nor explained in the journal publication. The incidence of outcome switching in follow-up studies rose to 70% when preceded by outcome switching in the corresponding initial RCT (P< 0.001). ConclusionIn this study, outcome switching occurred in 40% of follow-up publications of previously published RCTs. The majority is neither pre-specified nor explained.
Highlights
The incidence of outcome switching in follow-up studies rose to 70% when preceded by outcome switching in the corresponding initial RCT (P< 0.001)
Outcome switching in follow-up publications was significantly more likely if it was preceded by outcome switching between the protocol and the initial RCT publication, or if there was no protocol available (70% [19/27] vs 24% [12/51], P< 0.001)
Our results show outcome switching in 40% of the included follow-up publications, which is similar to previous research that shows changes in primary outcomes in 31–62% of RCTs [5,6,7,8,9]
Summary
In order to facilitate high quality reporting the Consolidated Standards of Reporting Trials (CONSORT) statement was first published in 1996 [3]. Outcome switching is defined as the selective reporting of pre-specified outcomes as well as new outcomes that are added after the start of the trial. Both types of outcome switching may lead to “cherry picking", where the choice for the reported outcome measure is derived from the data. This leads to reported treatment benefits that are more likely to be overestimated, or even entirely based on chance [5]
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