Rate-Force Index a+b A single figure that measures the forces of specific events, for example death, disease. mortality morbidity) a= the frequency with which an event has occurred during some specified period of time a+b= the number of person exposed to the risk of the event during the same period of time K=some number such as 100, 1000, 100,0007 Rate-Force Index • A single figure that measures the forces of specific events, for example death, disease. mortality & morbidity) • a= the frequency with which an event has occurred during some specified period of time. • a+b= the number of person exposed to the risk of the event during the same period of time • K=some number such as 100,1000,100,000 a k a b       +