The term rate of occurrence refers to the number of times an event or phenomenon occurs over a given period of time. It is related to two other terms, INCIDENCE and FREQUENCY. INCIDENCE is the number of new cases of a particular event or phenomenon that occur in a population over a given period of time. FREQUENCY is the number of times an event or phenomenon occurs in a population over a given period of time. Both INCIDENCE and FREQUENCY are used to measure the rate of occurrence of an event or phenomenon.