Calculate EER from FAR and FRR? I'm wondering if we have FAR and FRR scores for each threshold if we can compute an EER programatically?
Say we have:
FAR FRR
1.0 0.0
0.8 0.1
0.6 0.2
0.5 0.4
0.2 0.6
0.0 1.0

Can we compute the EER programatically?
 A: Yes, you can compute the EER from the FAR and FRR. Usually, the EER is just the error for FAR==FRR. In case there is no numeric value FAR==FRR (like in your provided example), you need to take a value in between the closest FAR and FRR values. There are multiple ways of obtaining such (none of them is perfect, as the information you seek is missing by definititon, so you can just get a close estimate). I've seen e.g.


*

*$EER=\frac{FAR+FRR}{2}$ with those single FAR and FRR values that minimize abs(FAR-FRR). In your case: $\frac{0.5+0.4}{2} = 0.45$.

*Using the line between the FAR and FRR values directly before and after FAR==FRR (in your case: the line between FAR1=0.5, FRR1=0.4, and FPR2=0.2, FRR2=0.6). The intersection of this line with the line [1,1] to [0,0] is frequently used as EER too.


Just for completeness: from my understanding, both approximations are necessarily very slightly pessimistic, as they do a linear approximation over a non-linear relation, towards more error.
