efficacy

[…]and this hath even made me ſuſpect the efficacy of reliques, to examine the bones, queſtion the habits and appurtenances of Saints, and even of Chriſt himſelf.

No method of verification known to science is applicable to the efficacy of prayer. […] If, then, the efficacy of prayer eludes the test of science, and if even uncertainty may rest upon the connectio

2005, Flay et al. Standards of Evidence: Criteria for Efficacy, Effectiveness and Dissemination DOI: 10.1007/s11121-005-5553-y Efficacy refers to the beneficial effects of a program or policy under op

Don't confuse "efficacy" with "efficiency".

The aim of this study was to evaluate the efficacy of acupuncture in the treatment of SAR through a randomized controlled trail.

This practice is of dubious efficacy.