Efficiency Vs Effectiveness: How do they differ?

Efficacy and effectiveness are two concepts related to assessing the health care innovations. These concepts were defined by famous British Clinical Epidemiologist, Archie Cochrane. Although, they sound and look same, there are some major differences between these two terms. Before looking at the differences, we must understand that the distinction between efficacy and effectiveness should be viewed as a spectrum, not a strict dichotomy.

Table of Contents

Now, let’s have a look the differences:

Efficacy	Effectiveness
Efficacy is the extent to which an intervention does more good than harm under ideal circumstances	Effectiveness assesses whether an intervention does more good than harm when provided under usual/practical circumstances
Efficiency measures the degree of success of an intervention in ideal conditions	Effectiveness measures the degree of success of an intervention under normal or usual circumstances
While assessing the efficacy of the study/intervention, the research question must be explanatory	While assessing the efficacy of the study/intervention, the research question must be pragmatic
Efficacy measures how well an intervention produces its desired result under perfect/ideal conditions	Effectiveness measure the real-world success, easiness and difficulties of an intervention
Efficacy describes how the intervention works in ideal, controlled or laboratory setting.	Effectiveness describes how the intervention works in real-world setting where different variables/factors cannot be controlled
Efficacy checks the success in ideal condition	Effectiveness checks the success in real world
It asks the question: Can a treatment/intervention work under ideal circumstances?	It asks the question: Does the treatment/intervention work in real world?
Efficacy studies provide a ground base for effectiveness studies. This is because efficacy studies show the effect of an intervention in an ideal condition. This will provide a base for effectiveness study to see the result in real world setting.	Effectiveness studies can be valuable to test whether and how much the results of efficacy trials are applicable to practical life.
Characteristic differences of efficacy studies and effectiveness studies:
Efficacy studies/trial are also known as explanatory trial	Effectiveness studies/trial are also known as pragmatic trial
Efficacy trials are used to study or see if the intervention has a specific effect	Effectiveness trials are used to study or capture the multi-factorial nature of interventions and inform the result of intervention in practical setting.
Efficacy trials have strict inclusion and exclusion criteria for study population	Effectiveness trials have limited exclusion criteria and it involves more heterogeneous population
Efficacy studies are usually conducted in large populations/large tertiary care which have more facilities, infrastructure and better technical equipment.	Effectiveness studies are usually conducted in more practical situations which are applicable to diverse population.
Intensive resources are dedicated to these studies	Less resources are dedicated to these studies
These studies use features such as randomization and blinding	These studies can be randomized but they are rarely blinded
It uses placebo	It may rarely use placebo
These studies do everything possible to maximize the chance of showing an effect of treatment/intervention	These studies allow the real-world factors to take place and try harder to duplicate the situations that will be encountered in real-world
In these studies, compliance is closely monitored and ensured	In these studies, compliance is not monitored closely and given less value
It has high internal validity	It has high external validity
The study is done following the protocol strictly	The study does not strictly limit to the protocols, rather is gives space for practical contexts
It usually has fewer missing data	It usually has more missing data
The outcome measures of efficacy studies are more objective	The outcome measures of effectiveness studies are more subjective
Study process is strictly defined	Study process is loosely defined
It has less bias and confounders as they are minimized	It has more bias and confounders. Moreover, the effect of bias and confounders is also substantial.
These studies/trials can establish the cause-effect relationship	These studies/trials can rarely establish cause-effect relationships