the.com/efficacy
Proof a thing works in a lab, before reality gets a vote.
means The capacity of something to produce its intended result under ideal, controlled conditions.
from From Latin efficacia, rooted in efficax, meaning powerful or effective, itself from efficere, to accomplish or bring about.
Not effectivenessEfficacy is the trial; effectiveness is the messy real world.
Vaccine math95% efficacy means risk cut, not 95 of 100 spared.
Older siblingPredates self-efficacy by centuries; psychologists borrowed it later.