While both formulae you offer seem reasonable, they ignore the timeframe in which calls were abandoned and how they are factored in the overall service level. Service level (as calculated by the ACD unit) is a better metric than plain vanilla percentage of abandoned calls, because it also considers the timing of answering calls and how soon callers abandon calls.
There are essentially 3 approaches to calculating service levels (which is sort of the inverse of abandoned calls). The choice of method depends on the call centers attitude towards abandoned calls do they represent a lost opportunity and therefore are of high value, or are they simply a fact of life and can be ignored
. As you can see from the following examples, the right choice can have a significant impact on your call centers statistics
Calls offered: 100
Answered within service level threshold: 70
Abandoned within service level threshold: 10
Exceeded threshold: 20
Service Level:
Abandoned calls ignored: 70 / (100 - 10) = 77.7%
Abandoned calls have negative impact: 70 / 100 = 70.0%
Abandoned calls have positive impact: (70 + 10) / 100 = 80.0%
Id be happy to answer further questions you might have.
Joe Barkai
www.DiagnosticStrategies.com