What is the difference between efficacy and efficiency?
Well, efficacy is whether it works or not... whether it has that
capacity. Efficiency is not whether it works, but how well it
works... how quickly, how many people have to be involved, etc. If
you cut down the amount of time it takes or the amount of workers
it takes, then you are improving efficiency.
Here are the links for the words on dictionary.com if you would
like to investigate further:
Efficacy is defined as 'that which brings about the
Efficiency, in engineering terms, is defined as 'the
ratio of a machine's output power to input power.