Efficacy: Efficacy refers to how well an intervention works and measures the ability of an intervention to produce a desired effect in a highly controlled environment. It is often assessed in randomized controlled trials. The goal of an efficacy study is to demonstrate that the intervention has a statistically significant effect on the outcome being measured
Effectiveness: Effectiveness refers to how well an intervention works under real-world conditions and it measures an intervention’s cost-effectiveness. effectiveness studies usually designed to evaluate whether an intervention is useful and practical when applied to real world situations, and they can provide valuable information on the feasibility of implementing interventions.
Efficiency: Efficiency refers to the cost-effectiveness of an intervention and measures the ratio of the resources required to achieve the desired outcome while using resources. Efficiency studies are to check if an intervention is worth the resources required to implement it