8
Threshold
Threshold means a value that is set to ensure the minimum accuracy
required to confirm a match with a finger template stored in a biometric
system.
The threshold setting establishes a balance between False Acceptance
Rate (FAR) and False Rejection Rate (FRR). FAR means the probability
that a biometric system will incorrectly identify a user or will fail to reject
an impostor. FRR means the probability that a biometric system will fail
to identify an enrolled user.
The threshold value is a global setting applied for all users. The default
threshold is set at 35. Raising the threshold value increases security but
increases the probability of a false rejection. Lowering the threshold
reduces security by increasing the possibility of a false acceptance. The
correct balance is vital for maximum security as well as usability. It is
possible that adjustments to the threshold value will be needed as you
begin using the biometric system.
If some users have persistent problems being accepted by a biometric
time clock, sometimes acceptance rates can be increased by first
inputting a User ID, then reading the finger. This is called a (1:1) “one
to one” verification. Greater success rates can be achieved because the
system now knows which specific finger template to compare.
Alternatively, the time clock can be set to the “one to one” verification
mode which then will require all users to input a User ID, followed by a
finger reading. The default threshold value for the “one to one” setting
is 15, but it too can be adjusted as necessary.
Table 1-1 shows some suggested threshold values to try but the others
can be set to achieve desired user acceptance rates.
