The sensitivity index or d' (pronounced 'dee-prime') is a statistic used in signal detection theory. It provides the separation between the means of the signal and the noise distributions, compared against the standard deviation of the signal plus noise distributions. For normally distributed signal and noise with mean and standard deviations and , and and , respectively, d' is defined as:
An estimate of d' can be also found from measurements of the hit rate and false-alarm rate. It is calculated as:
d' is a dimensionless statistic. A higher d' indicates that the signal can be more readily detected.
- Wickens, Thomas D. (2001) Elementary Signal Detection Theory, OUP USA. ISBN 0-19-509250-3 (Ch. 2, p. 20). Excerpts
- Interactive signal detection theory tutorial including calculation of d'.