D prime (d')

D prime (d') is a measure used in signal detection theory to quantify how well someone can distinguish between a signal (e.g., a target) and noise (e.g., background). It reflects the separation between the true signal and noise distributions, accounting for the person's ability to detect signals accurately while avoiding false alarms. A higher d' indicates better discrimination, meaning the person is more accurate in identifying signals versus noise. Conversely, a low d' suggests difficulty in telling the difference, with more errors. It provides a unified way to assess sensitivity independent of guessing or response bias.