She had already satisfied herself that he thought Harriet a beautiful girl, which she trusted, with such frequent meetings at Hartfield, was foundation enough on his side; and on Harriet’s there could be little doubt that the idea of being preferred by him would have all the usual weight and efficacy.
There are no more uses of "efficacy" in the book.
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The doctor weighed the efficacy of each treatment against potential side-effects.
They held hearings to investigate concerns about the safety and efficacy of the vaccine.