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Objectives To 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 setting Meta-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. Results Seventy-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 Conclusion In this study, outcome switching occurred in 40% of follow-up publications of previously published RCTs. The majority is neither pre-specified nor explained.

Publication bias (the tendency for studies with positive results to be more easily published than studies with null or negative results) and outcome switching (the adjustment of study aims to match results) have long been problematic in medical research. Recent legislation, protocol-registration sites, and agreements by medical journals have led to a reduction of these problems in medical research. In medical education specifically, however, there is no such legislation, registration, or agreement. This paper argues for the creation of such a registration site and agreement by medical education journals as a matter of ethical necessity.

This article was migrated. The article was marked as recommended. Publication bias (the tendency for studies with positive results to be more easily published than studies with null or negative results) and outcome switching (the adjustment of study aims to match results) have long been problematic in medical research. Recent legislation, protocol-registration sites, and agreements by medical journals have led to a reduction of these problems in medical research. In medical education specifically, however, there is no such legislation, registration, or agreement. This paper argues for the creation of such a registration site and agreement by medical education journals as a matter of ethical necessity.