Every yes-or-no judgement secretly mixes skill with bias

Developed from WWII radar operators trying to spot enemy blips in noise, signal detection theory showed that any yes/no judgement combines two separate things: how well you can actually detect a signal, and how cautious or trigger-happy you are about saying 'yes.' The framework now separates true skill from bias in medical scans, lie detectors and eyewitness lineups.

— David Green and John Swets, Signal Detection Theory and Psychophysics — Wiley, 1966