Efficacy is the effect outcome which is from the measurement under controlled or ideal conditions. The efficacy study, such as Randomized control trials, will be done under strict inclusion/exclusion criteria and intervention. The result from efficacy measurement might be limited to generalizations depending on the population included in the trial. However, bias in this type of research is controlled and the efficacy outcome could answer whether the intervention worked or not?
Effectiveness is the effect outcome which is from the measurement under real life conditions or in real clinical practice. Observational studies are able to measure effectiveness of the intervention.The effectiveness study will be done in more flexible environments compared to the efficacy study. Therefore, there is possibly bias, confounding and interfering with the results. However, heterogeneity of the population in the study can generate broader result application and answer the question “Does the intervention benefit the patient?”
Efficiency is the effect outcome which is from the measurement of the interventions’ benefit along with the cost consideration. Cost-benefit and cost effectiveness analysis are examples of studies where efficiency is measured. The cost consideration could be in terms of time, energy, or money. For instance, if there are two medicines with the same effectiveness, the one which is more costly could be considered less efficient in comparison with the one which is cheaper. Measuring efficiency could answer the question “Does the intervention work in the most economical way?”