Adverse event reporting system. Adverse event reporting system (AERS) is created to monitor a possible causal relationship between drug and event. The database contains the information about the entire list of medical products and of medical terms of adverse reaction. Each event is reported exactly once alone with the list of medical products prescribed to a patient at the point of event, say ``Rosinex & Ganclex,'' and the list of medical terms describing adverse events, say ``Nausea.''
Frequency of event. Each event is reported with the list of drug names and of adverse reactions, and the entire data are summarized in terms of the frequency of such events, denoted by . Note that a pair is not necessarily labeled as a valid association of model. For example, an adverse event of ``Rosinex & Ganclex'' and ``Nausea'' is reported, but the drug combination of Rosinex and Ganclex may not be necessarily the cause of nausea.
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