This approach to signal identification and refinement is similar in concept to proportional morbidity ratios (Rothman and Greenland, 1998). Basically, the number of reports of a given ADR or of a group of ADR terms is viewed as a proportion of all ADRs reported for that drug. The resulting measure can serve to highlight specific drug reactions or show a clustering of different reactions, all of which affect a particular organ or body system. Of perhaps greater utility, a drug's proportional distribution can be compared with that of other drugs in the same pharmacologic class or with drugs from other classes used to treat the same indication. From this type of analysis, one might observe that a particular antibiotic has a relatively high proportion of skin-related ADRs compared with other class members. As with proportional morbidity ratios, proportional distributions are useful in a qualitative sense, revealing potential ''problem areas'' for a drug. However, they do not contribute to our understanding of ADR incidence.
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