Effectiveness

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Effectiveness means the capability of producing an effect.

In mathematics, effective is sometimes used as a synonym of algorithmically computable.

In physics, an effective theory is, similar to a phenomenological theory, a framework intended to explain certain (observed) effects without the claim that the theory correctly models the underlying (unobserved) processes. An example is an effective field theory that "pretends" that certain effects are caused by a field even if it is known that this is not actually the case. In a way, any theory of Physics is fundamentally an effective theory, since there is no meaningful distinction of observables and reality within the scope of Physics (see also FAPP, cogito ergo sum, Phenomenalism, Pragmatism).

In heat transfer, effectiveness is a measure of the performance of a heat exchanger when using the NTU method.

In medicine, effectiveness relates to how well a treatment works in practice, as opposed to efficacy, which measures how well it works in clinical trials or laboratory studies.

In management, effectiveness relates to getting the right things done. Peter Drucker reminds us that effectiveness is an important discipline which “can be learned and must be earned.”^[1]

The word effective is sometimes used in a quantitative way, "being very or not much effective". However it does not inform on the direction (positive or negative) and the comparison to a standard of the given effect. Efficacy, on the other hand, is the ability to produce a desired amount of the desired effect, or success in achieving a given goal. Contrary to efficiency, the focus of efficacy is the achievement as such, not the resources spent in achieving the desired effect. Therefore, what is effective is not necessarily efficacious, and what is efficacious is not necessarily efficient.

An ordinary way to distinguish among effectiveness, efficacy, and efficiency:

• efficiency: doing things in the most economical way (good input to output ratio)
• efficacy: getting things done, i.e. meeting targets
• effectiveness: doing "right" things, i.e. setting right targets to achieve an overall goal (the effect)
• (effectivity: mostly synonym to effectiveness; usage is rather rare)

1. ^ Drucker, Peter F. The Effective Executive The Definitive Guide to Getting the Right Things Done (Harperbusiness Essentials). New York: Collins, 2006.