What is the difference in meaning between the above words? Are they interchangable? I have seen several instances where efficacy has been used where it seems that efficiency is the correct term. Please forgive me if this question has been asked elsewhere. If anyone could point me in the direction of an explanation I'd be very grateful.

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    Welcome to English Language and Usage. Please read the question which was closed as general reference. Is there any difference in meaning between 'efficacy' and 'efficiency'?. – user140086 Feb 26 '16 at 17:07
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  • Would you like me to delete this question? Apologies for any rule-breaking. – maguirenumber6 Feb 26 '16 at 17:24
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    It is up to you. You didn't break any rule as you were not aware of it. Please try to read the guidelines of our Help Center. You need to show us some research efforts on the two words and tell us what you understand and what you don't. That will make your question on-topic. Good luck. – user140086 Feb 26 '16 at 17:27
  • I'd usually say it's a good idea not to delete questions closed as duplicates, because the fact of there being different titles (and other indexed text) might help future posters find a duplicate before asking again. In this case I don't think that's a significant factor, but I still see no reason to delete the later question. – FumbleFingers Feb 26 '16 at 17:33

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