Efficiency, Effectiveness, Efficacy ?


  • Effectiveness is the extent to which planned outcomes, goals, or objectives are achieved as a result of an activity, strategy, intervention or initiative intended to achieve the desired effect, under ordinary circumstances (not controlled circumstances such as in laboratory).
    Example: A vaccine is effective when it is capable to produce the desired effect (protection against disease) in the population, under ordinary circumstances.
  • Being effective means achieving organizational goals. Being efficient means achieving goals with little wasted resources. Effectiveness comes first.


  • Efficiency is the ratio of the output to the inputs of any system. An efficient system or person is one who achieves higher levels of performance (outcome, output) relative to the inputs (resources, time, money) consumed. 
    Examples: Worker A moved 16 boxes from the truck to the store in one hour and worker B moved 9 boxes in one hour. Worker A is more efficient than worker B. Car T uses 10 gallons to travel 150 miles, car F uses 13 gallons to travel 150 miles. Car T is more fuel efficient than car F.


  • Efficacy is the extent to which a specific intervention, procedure, or service produces the desired effect, under ideal conditions (controlled environment, lab circumstances). Efficacy = Effectiveness. Only the circumstance.
    Example: The efficacy of vaccine A was achieved under ideal lab circumstances, yet, its effectiveness needs to be shown.”efficiency = efficacité et effectiveness = bon fonctionnement”

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