Effectiveness n. : The quality of being effective.

Example:
What types of things reduce the Effectiveness of birth control?

Taxonomy
effectiveness, efficacy, free encyclopedia, Physics, effective theory, theory, synonym, efficiency, measure, right things, desired effect, achieving, efficacious, targets, search, free dictionary, capability, framework.

Defination from the web:
effective is sometimes used as a synonym of algorithmically computable. ... In heat transfer, effectiveness is a measure of the performance of a heat exchanger when using the NTU method. ... In management, effectiveness relates to getting the right things done. ...