FAR and FRR: security level versus ease of use

FAR and FRR. Anyone looking to assess or compare the performance of biometric security systems cannot avoid these terms. In this article, we explain what FAR and FRR mean, how they affect each other and their implications for security level and ease of use.
Let us start with the definitions. The performance of biometric systems is expressed in terms of the following error probabilities:

  • False Acceptance Rate (FAR): the percentage of recognitions where someone is wrongly recognised (false acceptance).
  • False Rejection Rate (FRR): the percentage of recognitions where someone is wrongly not recognised (false rejection).

How do FAR and FRR influence each other?

As the number of false acceptances (FAR) decreases, the number of false rejections (FRR) will increase. And vice versa. See the image below. The point at which the lines cross also has a name: the Equal Error Rate (EER). That is where the percentage of false acceptance and false rejection is equal.

What does this mean for the security level and ease of use?

When aiming for the lowest possible FAR, the FRR is likely to become much larger. In other words, the more secure the access control, the lower the ease of use because users are mistakenly not recognised by the system. The reverse is also true: greater ease of use due to a lower FRR? Then the system is also likely to become more unsafe (higher FAR).
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Setting the FAR and FRR in the software…

The FAR and FRR can usually be tuned in a security system’s software by adjusting these criteria to be more or less stringent. From the information above, we can conclude that this leads to a more secure (but less user-friendly) or, on the contrary, a more insecure (but more user-friendly) system.

… and the problem with that

There are few systems on the market that facilitate both a high level of security and user-friendly access control. If such a system is not chosen, then better ease of use is often chosen at the expense of lower security. You can imagine the trade-off: “Surely, you don’t want to put people through queuing at the door because the system is not working properly. They may have been in traffic jams all morning and not had coffee yet…”.

Of course, this may be acceptable to users in some situations. But obviously not in situations where a high level of security is expected. This is the problem: exactly how the software is set up is often not visible to the user. This can create a false sense of security.

Something to watch out for: visibility of the FAR and FRR.

Like many security experts, we take the view that the FAR and FRR should not be changed invisibly. We believe the visibility of this belongs in the configuration of a system. In any case, it is something to look out for when choosing an access security system!
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