While translating from English into Russian (and vice versa) I always struggle with two terms: effectiveness and efficiency.
For exmple if we are talking about production (oil and gas, metals etc) Is it "operating efficiency" or "effectiveness"?
"operating efficiency" can be correct as a compound noun.
Effective = it produces the results that are intended
Efficient = it uses resources economically and/or quickly
It is possible for something to be effective but not efficient. But it is not usually possible for something to be efficient but not effective.
e.g. My car gets me from A to B when I need and so it is effective. But it doesn't go very fast and it uses a lot of petrol - so it is not efficient.