Efficacy - as the others wrote, but with the following. It is the best effect that you can see from the intervention under controlled and ideal conditions. So, for a drug, we pick everybody within a certain age range, with a very tight definition of the disease, closely monitor the patients, make sure they are taking the drug properly and see if the drug works. For example, you might get 20% improvement in the disease under ideal conditions. Effectiveness - in real life conditions, we never have ideal conditions. There are always things which can go wrong e.g. patient forgets to take the medicine, cannot tolerate side effects, hospital can't afford to give drug etc. So although, the drug has a high efficacy, it's effectiveness (the desired effect it has during real life conditions), is lower than the 20% efficacy.

efficacy - more used in scientific, clinical trial articles, if you want to test the efficacy of certain drugs, to see if they can cure certain symptoms. effectiveness is broader than efficacy - it means whether the method you use is "effective" or not to reach your goal, no matter how long it takes. efficiency - it is more used to emphasize you complete something in the shortest time possible. e.g.. In terms of typing she is more efficient than him. This means she can type 100 words within a shorter period of time than him To raise a wall against refugees will not be effective - it means this method will NOT work. Time here is less emphasized.

Efficacy-the ability to produce a desired or intended result. "there is little information on the efficacy of this treatment" Efficiency-the state or quality of being efficient. "greater energy efficiency" synonyms: organization, order effectiveness-the degree to which something is successful in producing a desired result; success. "the effectiveness of the treatment", synonym- success

Hi Anna, I hope this link help you, and I prefer the first one 1-http://www.hayajneh.org/glossary/vocabulary/e/EfficiencyEffectivenessEfficacy.html 2-http://www.australianprescriber.com/magazine/23/6/114/5