"In any epidemic... let us suppose five hundred of the sick, taken indiscriminately, to be subjected to one kind of treatment, and five hundred others, taken in the same manner, to be treated in a different mode; if the mortality is greater among the first, than among the second, must we not conclude that the treatment was less appropriate, or less efficacious in the first class, than in the second ? It is unavoidable; for among so large a collection, similarities of condition will necessarily be met with, and all things being equal, except the treatment, the conclusion will be rigorous."