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No evidence of important difference in summary treatment effects between COVID-19 preprints and peer-reviewed publications: a meta-epidemiological study

Davidson et al., Journal of Clinical Epidemiology, doi:10.1016/j.jclinepi.2023.08.011
Sep 2023  
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Meta-epidemiological study including 37 meta-analyses with 114 RCTs assessing pharmacological treatments for COVID-19, showing no evidence of an important difference in meta analysis results between preprints and peer-reviewed publications.
Davidson et al., 21 Sep 2023, peer-reviewed, 5 authors. Contact:
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No evidence of important difference in summary treatment effects between COVID-19 preprints and peer-reviewed publications: a meta-epidemiological study
Mauricia Davidson, Theodoros Evrenoglou, Carolina Graña, Anna Chaimani, Isabelle Boutron
Journal of Clinical Epidemiology, doi:10.1016/j.jclinepi.2023.08.011
Objectives: Preprints became a major source of research communication during the COVID-19 pandemic. We aimed to evaluate whether summary treatment effect estimates differ between preprint and peer-reviewed journal trials. Study Design and Setting: A meta-epidemiological study. Data were derived from the COVID-NMA living systematic review ( up to July 20, 2022. We identified all meta-analyses evaluating pharmacological treatments vs. standard of care or placebo for patients with COVID-19 that included at least one preprint and one peer-reviewed journal article. Difference in effect estimates between preprint and peer-reviewed journal trials were estimated by the ratio of odds ratio (ROR); ROR !1 indicated larger effects in preprint trials. Results: Thirty-seven meta-analyses including 114 trials (44 preprints and 70 peer-reviewed publications) were selected. The median number of randomized controlled trials (RCTs) per meta-analysis was 2 (interquartile range [IQR], 2e4; maximum, 11), median sample size of RCTs was 199 (IQR, 99e478). Overall, there was no statistically significant difference in summary effect estimates between preprint and peer-reviewed journal trials (ROR, 0.88; 95% CI, 0.71e1.09; I 2 5 17.8%; t 2 5 0.06). Conclusion: We did not find an important difference between summary treatment effects of preprints and summary treatment effects of peer-reviewed publications. Systematic reviewers and guideline developers should assess preprint inclusion individually, accounting for risk of bias and completeness of reporting.
Supplementary data Supplementary data to this article can be found online at
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