Efficacy, effectiveness, and efficiency

 The concepts of efficacy, effectiveness, and efficiency are frequently misunderstood. They all pertain to the outcome of a medical intervention, but it is crucial to comprehend their differences accurately.

Efficacy refers to whether an intervention produces more benefit than harm when tested under tightly controlled, ideal circumstances, such as strict inclusion/exclusion criteria, close monitoring, and high adherence to the treatment protocol. This effect is typically investigated in a classical randomised trial designed for high internal validity, an explanatory trial (1).

Effectiveness refers to how well an intervention works in everyday clinical practice with a more diverse patient population including comorbidities, inconsistent adherence, and varying follow-up care. This effect is often investigated in a pragmatic trial, prioritizing external validity (representativity) instead of internal validity.

The distinction between efficacy and effectiveness is important because an intervention may show high efficacy in a population of relatively healthy and adherent trial participants but perform poorly when used broadly. Furthermore, the effectiveness of an intervention is often difficult to assess. For example, the efficacy of vaccine can be established in controlled trials with susceptible volunteers, but the effectiveness in the general population has to be investigated in observational studies. These investigations generate more uncertain results because of potential confounding and other forms of bias that are unavoidable in observational studies.

Efficiency, finally, refers to whether the health gains of an intervention are sufficient relative to the consumed resources (2). This is a health economic issue. It usually includes the estimation of an incremental cost-effectiveness ratio (ICER) that shows how much additional cost is required to obtain an additional unit of health outcome. The ICER is an essential tool for judging efficiency, but efficiency encompasses more than estimating ICERs.

References

1. Ernst, E. and Pittler, M.H. (2006), Efficacy or effectiveness?. Journal of Internal Medicine, 260: 488-490. https://doi.org/10.1111/j.1365-2796.2006.01707.x

2. Jacobs, Rowena, Smith, Peter C. and Street, Andrew, (2006), Measuring Efficiency in Health Care, Cambridge University Press, https://EconPapers.repec.org/RePEc:cup:cbooks:9780521851442.

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