Cost Effectiveness

Desired impact or effect produced per unit of cost. Effectiveness refers to the relation between system and environment and to the system's desired impact on its environment. Efficiency, on the other hand, refers to the relation between system input and system output. An efficient system is not necessarily effective, whereas an effective system is not necessarily efficient. Relating effectiveness to costs, however, permits to some extent to include the aspect of (cost-)efficiency. (Hornung )