Usability is the primary performance dimension of the security process. Get it right and both security and efficiency flow, but usability is all wrapped up in human psychology. It’s a complicated subject deeply linked to behaviour, not just that of customers, but also of call-centre agents.
While there are many aspects to the usability of a security process, the simplest measure is how often someone who is who they claim to be is able to complete it successfully. The inverse of this, and the source of greatest customer frustration, is known as a false reject (FR): a genuine caller who is unable
to access the service because they can’t successfully complete the security process.
Different identification and authentication methods will have different rates of FR depending on their design and the factors they use, but the overall usability of an organisation’s process will also depend on how frequently each of these methods is used. If you work on the basis that nearly all callers to a call centre are who they claim to be, then the FR rate is simply the number of customers who are denied or restricted service as a result of failing to complete the process.
There is more information about improving Usability here: Improving the Usability of your Call Centre Security Experience