• Graham D Cole, Alexandra N Nowbar, Michael Mielewczik, Matthew J Shun-Shin, and Darrel P Francis.
• International Centre for Circulatory Health, National Heart and Lung Institute, Imperial College London W2 1LA, UK g.cole@imperial.ac.uk.
• BMJ. 2015 Jan 1;351:h4708.

ObjectivesTo compare the frequency of discrepancies in retracted reports of clinical trials with those in adjacent unretracted reports in the same journal.DesignBlinded case-control study.SettingJournals in PubMed.Population50 manuscripts, classified on PubMed as retracted clinical trials, paired with 50 adjacent unretracted manuscripts from the same journals. Reports were randomly selected from PubMed in December 2012, with no restriction on publication date. Controls were the preceding unretracted clinical trial published in the same journal. All traces of retraction were removed. Three scientists, blinded to the retraction status of individual reports, reviewed all 100 trial reports for discrepancies. Discrepancies were pooled and cross checked before being counted into prespecified categories. Only then was the retraction status unblinded for analysis.Main Outcome MeasureTotal number of discrepancies (defined as mathematically or logically contradictory statements) in each clinical trial report.ResultsOf 479 discrepancies found in the 100 trial reports, 348 were in the 50 retracted reports and 131 in the 50 unretracted reports. On average, individual retracted reports had a greater number of discrepancies than unretracted reports (median 4 (interquartile range 2-8.75) v 0 (0-5); P<0.001). Papers with a discrepancy were significantly more likely to be retracted than those without a discrepancy (odds ratio 5.7 (95% confidence interval 2.2 to 14.5); P<0.001). In particular, three types of discrepancy arose significantly more frequently in retracted than unretracted reports: factual discrepancies (P=0.002), arithmetical errors (P=0.01), and missed P values (P=0.02). Results from a retrospective analysis indicated that citations and journal impact factor were unlikely to affect the result.ConclusionsDiscrepancies in published trial reports should no longer be assumed to be unimportant. Scientists, blinded to retraction status and with no specialist skill in the field, identify significantly more discrepancies in retracted than unretracted reports of clinical trials. Discrepancies could be an early and accessible signal of unreliability in clinical trial reports.© Cole et al 2015.

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