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FDA MedWatch 3500A form（For use by user-facilities，importers，distributors and manufacturers for MANDATORY reporting）：http：/ / www . fda . gov/downloads/Safety/MedWatch/Ho DownloadForms/ucm082728 . pdf.J Howick，P Glasziou，J Aronson . The evolution of evidence hierarchies：what can BradfordHill ’ s guidelines for causation contribute？Clin . Pharmacol . Ther，1977，21.I . Background，description and instructions for use .Int J Clin Pharmacol ther Toxicol，1980，381-388.