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Weighted averages

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  • #32523
    Lee H.

    I am a supervisor in a multi-queue call center. Currently, our department that calculates the total call center service level for all queues uses a add and divide method to calculate service levels.

    Example, if our queues end the day with a 75%, 63%, 97% and 84% service leveI, the overall call center ends up with a 79.75% service level for the day. I understand there is a “weighted average” formula that takes into account the total number of calls per queue, plus the service level in each queue in calculating an overall service level.

    What is the pro’s and con’s of using either method for caulculating overall service level? Any information would be greatly appreciated.


    Lester Bromley

    The accepted method is to total all the calls that were answered within the SLA target and divide this by the total number of calls answered to produce the overall SLA percentage. Some switches will report this figure directly, e.g. the Lucent Definity defines the variable ACCEPTABLE in the VDN and Skill tables to count the number of calls answered within SLA. Otherwise multiply the number of calls answered in a queue by the SLA percentage for that queue to get the acceptable calls figure, add these together and divide by the total answered.

    This method is also used to calculate the monthly average from the daily figures for that month.

    (Note that some switches report the SLA as a percentage of offered calls rather than answered calls in which case use the offered calls figure instead)


    The service level philosophy in our call center is simple. You can’t just keep adding staff to solve customer contact issues/problems. I think you ‘ve got to look at more effective solutions, by combining the skills ,technology and operational efficiencies to mangage a complex inbound service. In our skills-based routing environment, we have specialized groups, so we run interactive calculations. The Erlang-C method remains an accurate tool and it will probably always be around for teaching people queuing dynamics.


    By following the method you are today, you are “averaging averages” which will not give you an accurate number. You must use a “weighted” average to accurately calculate your true call center service level for all Queues.

    Hope this helps.

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