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' = Z(hit rate) - Z(false alarm rate),