Efficacy is the ability of something to produce the right result — how well it works at the job you gave it. You will see it all the time in medicine and science: the efficacy of a vaccine, a drug, a teaching method. It is a noun, and it is formal.

efficacy是 the ability of something to produce the right result某樣東西能不能達成該有效果的能力——how well it works at the job you gave it也就是它把交付的工作做得多好。you will see it all the time in medicine and science在醫學和科學領域常常看到：the efficacy of a vaccine, a drug, a teaching method疫苗的療效、藥物的療效、教學方法的成效。it is a noun這是個名詞，and it is formal而且是正式用語。

A researcher asks about efficacy; a parent at the table just asks, “Does it work?” Efficacy does not, by itself, tell you about side effects, cost, or speed. A treatment can have high efficacy in a test and still be hard to use in real life.

a researcher asks about efficacy研究者問的是療效；a parent at the table just asks, “Does it work?”餐桌上的家長只會問「這有用嗎？」efficacy does not, by itself, tell you about side effects, cost, or speed光是療效本身不會告訴你副作用、成本，或速度。a treatment can have high efficacy in a test and still be hard to use in real life一種治療可能在試驗裡療效很高，實際生活中卻很難使用。

The trap sitting beside it is efficiency. Efficiency is about little waste. Efficacy is about the result. A factory can be efficient (fast, little leftover) and still make the wrong product; a slow medicine can still have strong efficacy.

the trap sitting beside it旁邊那個容易搞混的陷阱字 is efficiency就是 efficiency。efficiency是關於 little waste很少浪費。efficacy是關於 the result有沒有效果。a factory can be efficient (fast, little leftover) and still make the wrong product一間工廠可以很有效率（快、沒什麼剩料），卻還是做錯產品；a slow medicine can still have strong efficacy一種藥雖然起效慢，卻可能療效很強。

Though actually, even careful writers mix the two, so it is worth slowing down when you see either word in a paper.

though actually不過事實上，even careful writers mix the two連小心的作者都會把這兩個字搞混，so it is worth slowing down when you see either word in a paper所以看到論文裡出現任何一個字，都值得放慢速度想一下。