The ratio between incidence among exposed and nonexposed persons is called-

.relative risk also called as risk ratio ,is the ratio of the incidence of the disease or death among exposed and incidence among non exposed.it is a direst measure of strength of association between suspected cause and effect.RR of one indicates no association,it must also be noted that risk does not necessarily imply causal association ref:park&;s textbook,ed22,pg no 75