has numerator has denominator ratio-based measure of association incidence rate incidence rate ratio A measure of association that is the ratio of two incidence rates. Brian S. Alper, Kenneth Wilkins, Joanne Dehnbostel, Muhammad Afzal IRR Incidence Rate (SEVCO STATO_0000680) is defined as: A rate in which the number of new events per total at risk is divided by an interval of time. The incidence rates may refer to the same event comparing two different groups, or the same group comparing two different events Philippe Rocca-Serra ready for release