What Measure Is Most Important?

When looking at biometric systems, it is easy to get lost in all the statistical measures available. To decide what measure is most important to your choice of a biometric system, its use needs to be defined as follows :

• Define the user population.

• Is the application for verification or identification?

• Are other means of authentication available?

• What is the importance of the biometric authentication?

• Is it driven by convenience and ease of use?

Define the User Population

When implementing a biometric system, the user population needs to be defined based on age, profession, or other population-specific characteristics. If the population is skewed toward the elderly or very young, then there is a concern over the success of the enrollment. In this case, a biometric system with a low FTE would be the most appropriate choice, so that you can be assured that a large percentage of the population will be enrolled. Also, if the professions of the population could affect the ability to enroll (e.g., people who work with their hands may have a harder time using finger-based biometrics), the FTE needs to be the most important measure.

Is the Application for Verification or Identification?

The use of a biometric system can suggest what biometric measures should be most important. If the biometric system is going to be used for verification (i.e., users will make claims of their identity), then it is most important that false rejections are minimized. In this case, a system that provides a very low FRR would be best. The choice of the FRR is based on the fact that a one-to-one match must take place. By reducing the set of biometrics that may be falsely matched against, the FRR becomes the most important measure.

If the biometric system is going to be used for identification (i.e., the users are not making claims about their identity), false authentications are most important. In this case, a system that provides a very low FAR would be best. The choice of the FAR is based on that fact that it is more important to properly identify a user than to ensure that the user is not falsely rejected. The set of biometrics to be compared against cannot be pared down. Thus, we want to minimize the possibility of a false authentication, and so the FAR becomes the most important measure.

Are Other Means of Authentication Available?

It is well-known that for any biometric system implemented, 3 “5% of the population base will not be able to use the system. If other authentication methods are not available or prove more costly to use and support, then another biometric system must be chosen that minimizes the exceptions. To minimize the exceptions, the system needs to be analyzed to see if the inability to use the system comes from the inability to enroll or to verify. If it is a case of not being able to enroll, then the FTE of the biometric system needs to be as low as possible. If it is a case of not being able to verify, then it is necessary to determine whether the exception threshold for authentication can be lowered . In this case, if the answer is yes, then we want a system with a lower FRR. This way, the user is less likely to be rejected.

What Is the Importance of the Biometric Authentication?

A biometric system controlling access to company secrets often requires a different biometric measure than a system controlling access to a user's personal address book. In the case where the biometric system is controlling access to sensitive information or a physical area, we should be more concerned about the FAR. In this case, the chance of the user's having to possibly attempt more authentications (and therefore decreasing user convenience) is of less importance than a false acceptance. If, on the other hand, the biometric system has been implemented for reasons of pure convenience only, then it is more important to minimize the FRR.

In the case where a biometric system is protecting something of importance and the user population is also demanding increased security, then the EER needs to be evaluated. This measure will give a good comparison of the tradeoff between convenience and security. Thus, the lower the EER, the more likely that the biometric system will meet the known requirements.

Is It Driven by Convenience and Ease of Use?

If a biometric system is driven by convenience and ease of use, then minimizing the FRR or having a low FTE becomes more important. Having a low FRR implies that the biometric system is willing to allow a higher level of false authentications. Having a low FTE means that more of the population will be able to use the biometric system as a convenience.