The quantity s is a log odds ratio. It tells us about the subject's ability to discriminate between faces they know and faces they don't.

`H` is the proportion of hits out of the group of faces they have seen. They have seen 20 + 5 faces = 25 so`...

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The quantity s is a log odds ratio. It tells us about the subject's ability to discriminate between faces they know and faces they don't.

`H` is the proportion of hits out of the group of faces they have seen. They have seen 20 + 5 faces = 25 so` `

`H = 20/25 = 4/5`

`F` is the proportion of faces they think they know out of of the group they haven't seen; the proportion of false positives. They have seen 10 + 15 = 25 faces they don't know so

`F = 10/25 = 2/5`

We can compute `s` from this and test whether `s` is significantly different from 1/2 (there is no difference between their recognition of faces they should know and faces they haven't seen before) by computing the standard error of `s` and checking that the lower limit of the confidence interval is greater than 1/2.

**We have H = 4/5 and F=2/5**