rate incidence rate A rate in which the number of new events per total at risk is divided by an interval of time. Brian S. Alper, Harold Lehmann, Joanne Dehnbostel, Kenneth Wilkins, Muhammad Afzal Incidence is defined as a proportion in which the numerator represents new events and the denominator represents the total at risk for events. Rate is defined as a ratio in which the numerator represents any quantity and the denominator represents an interval of time. The interval of time used for the denominator may be data-dependent when the duration of observation varies across the observations. In the method for calculating incidence rate (described at https://www.cdc.gov/csels/dsepd/ss1978/lesson3/section2.html), the numerator is the "Number of new cases of disease or injury during the specified period" and the denominator is the "Time each person was observed, totaled for all persons" adapted from: https://www.cdc.gov/csels/dsepd/ss1978/lesson3/section2.html and NCIt: Incidence Rate = The frequency of new occurrences of an event during a specified time period. average hazard rate incidence density ready for release