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What's the difference between:

efficacy, effectiveness, efficaciousness, efficiency

Which one should I use to describe the general capability of a system to generate expected, good results in an efficient manner? Basically, "how well it works all things considered". I'm currently using Several experiments were performed to examine the efficacy of the system. I contemplated using effectiveness, but I'm interested in not only how effective the solution is but also how efficient it is. (I believe the difference between effectiveness and efficiency to be that efficiency is concerned with the amount of consumed resources and effectiveness with the capability of producing correct results or solving the problem.)
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That's about how I think of them, too. I'd stick with efficacy. Certainly not 'efficaciousness'.
Comments  
Thanks, MM. I lost track of this post because it was moved.