Therapeutic index of a drug is a measure of its?

Therapeutic Index tells about the safety margin of drug; narrow therapeutic index means unsafe drug. TI : LD50/ED50 *LD50 : lethal dose in 50% of population.*ED50 : effective dose in 50% of population or median effective dose.*LD50 and ED50 can be calculated by plotting a quantal DRC. * In this Quantal DRC, x-axis represents the log dose and y-axis represents the percentage of population responding.* Graded dose response curve tells about the potency and efficacy of a given drug in a paicular individual.