Definition. Verifier error rates [ftip-005Z]

Let \(S\in \{0,1\}\) be an independently defined success label and \(A\in \{0,1\}\) the verifier's accept decision on the same outcome. The false-accept and false-reject rates are

\[ \eta _+=\Pr (A=1\mid S=0), \qquad \eta _-=\Pr (A=0\mid S=1). \]

Both rates are conditional on the task and outcome distribution used for the audit. They are undefined when the conditioning event has probability zero.