“Approximately half of studies published on new medical treatments leave out at least some of the adverse effects they uncovered, according to a recent analysis in PLOS Medicine.”
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Golder S, Loke YK, Wright K, Norman G (2016) Reporting of Adverse Events in Published and Unpublished Studies of Health Care Interventions: A Systematic Review. PLoS Med 13(9): e1002127. https://doi.org/10.1371/journal.pmed.1002127