Effectiveness

n. efficiency, productivity; impressiveness, quality of being striking

Effectiveness means the capability of producing an effect. 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).
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Noun
1. power to be effective; the quality of being able to bring about an effect
(synonym) effectivity, effectualness, effectuality
(antonym) ineffectiveness, ineffectualness, ineffectuality
(hypernym) power, powerfulness
(hyponym) incisiveness, trenchancy
(attribute) effective, effectual, efficacious
2. capacity to produce strong physiological or chemical effects; "the toxin's potency"; "the strength of the drinks"
(synonym) potency, strength
(hypernym) power, powerfulness
(attribute) potent, strong

(n.)
The quality of being effective.
  

The state of having produced a decided upon or desired effect.