d' (d-prime)

D' (d-prime) is a measure from signal detection theory that quantifies how well someone can distinguish between two different signals or conditions—like detecting a faint sound or identifying a cancer spot. It considers both the person's ability to correctly identify the signal (hits) and the tendency to mistakenly say the signal is present when it's not (false alarms). A higher d' indicates better discrimination ability, meaning the person can more accurately tell the difference. Essentially, it’s a standardized score that reflects the sensitivity or perceptual clarity between signal and noise.