Consider this 2x2 contingency table.
The Proportional Reporting Ratio, PRR, is one of the disproportional analysis methods used for analyzing drug-adverse events for signal detection. The formula is,
This is also written as,
Look at the top of the equation, A / (A + B). This is the ratio of the adverse event of interest vs. all other adverse events for the drug under investigation.
The bottom of the equation, (C / (C+D)), is the same, but for one or more drugs compared to the drug under investigation.
If the ratios are the same (e.g., 0.125 for both or 1/8th of every adverse event is the adverse event of interest for the drug under investigation and other drug groups used for the comparison), the PRR is 1, i.e., the occurrence of the adverse event of interest is at the same rate as the other drugs. If the ratios differ, the PRR will be higher than or lower than 1, depending on which ratio is higher. The PRR will be higher than 1 if the ratio of the adverse event of interest is reported more for the drug under investigation than for other drugs, and vice versa if the PRR is lower than 1.
Table: The ratio of adverse events for the drug under investigation over other drugs vs. PRR
If the PRR is 2, the ratio of adverse events reported is twice as high for the drug under investigation than for the comparison drug group. This is significant and should be considered for further follow-up analysis.
Ref: PRACTICAL ASPECTS OF SIGNAL DETECTION IN PHARMACOVIGILANCE - Report of CIOMS Working Group VIII
Comments