# #StackBounty: #psychometrics #signal-detection #d-prime How do I calculate d' from experimental data?

### Bounty: 50

In Signal Detection Theory, d’ is defined by the z-scores of Hits and False Alarms:

d’ = z(Hits) – z(False Alarms).

Say the task is to detect if a certain object is present in a series of pictures, and for one particular subject we have a hit rate of 0.9 and a false alarm rate of 0.2.

Now, the z-score would be typically calculated by $$frac{X-mu}{sigma}$$.
The stimulus is as described however presence/absence of an object (without any changes in stimulus intensity). It is hence not clear to me what $$mu$$ and $$sigma$$ could be – or do we simply assume a standard normal distribution to calculate the z-scores?

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