Question

In four sentences please answer this question:

What is the difference between effectiveness and efficacy? Is efficacy always an indicator of effectiveness?

Answer 1

Effectiveness is the degree to which something is successful in producing a desired result; success and the efficacy is the ability to produce a desired or intended result.

Intervention studies can be placed on a continuum,with a progression from efficacy trials to effectiveness trials. Efficacy can be defined as the performance of an intervention under ideal and controlled circumstances, whereas effectiveness refers to its performance under 'real-world' conditions.

Efficacy is the effect in perfect conditions, effectiveness is the effect in the real world. You could also consider efficiency, which is a measure of cost-effectiveness. In the realm of clinical studies, the difference boils down to how strictly controlled a study

efficacy is not always an indicator of effectiveness since it is the effect in perfect conditions.