The present method of determining potency of anthelmintics utillizes the worm excretion rate and egg extermination rate, but neither of the values alone is enough to express the potency of a drug. For this reason, various indeces were formulated and the following gave a fairly satisfactory results:
Index=Total points before prescription-Total points after prescription/Total points before prescription
where 0 point is the state in which no egg is found in one field of vision under the microscope, 2 points for 1-5 eggs, 3 points for 6-10 eggs, 4-points for 11-15 eggs, and increasing by 1 point thereafter for every 5 eggs found.