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Help in calculating arrival and service time

Six Sigma – iSixSigma Forums Operations Call Centers Help in calculating arrival and service time

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  • #53548

    Dr. Steve Pollock, ASQ Fellow
    Participant

    Need some advice about how to calculate a) average and standard deviation “service time” and b) average and standard deviation “interarrival time” in minutes. Am evaluating a waiting line model.

    Let’s say we have data for a typical day (see attached file).

    Would like comments on approach to take. [file name=Call_Center_analysis.xls size=15360]https://www.isixsigma.com/images/fbfiles/files/Call_Center_analysis.xls[/file]

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    #190651

    French
    Member

    What do you hope to accomplish with the model? The problem you’re trying to solve will affect the appraoch to the model.

    The data you’ve included is summary data, I recommend using call level details to calculate these statistics. Call level details allow you to see the variabilty and better represent that in your model.

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    #190652

    Dr. Steve Pollock, ASQ Fellow
    Participant

    Yes, I agree that individual data rather than summary data would be better to see the variation, but if all I have at this point is summary data, I would like to leverage it somehow. The objective is to see if the current system: phone, people, and performance supports the call volume.

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    #190655

    French
    Member

    You can’t get to standard deviation from this level of detail. Average agent time for all call types is the summed product of the CSR and % frequency – or about 72 seconds per call. Call duration is generally a pretty skewed distribution – call center models I’ve built have been more accurate using median instead of mean, which you can’t get from this data. It may also make sense to look at each call type separately, rather than this consolidated average – especially if all agents can’t field all call types.

    To get an approximate average interarrival time you could divide the duration of each time period (30 minutes) by the number of calls, so for 6:30 AM it would be 1:22 between calls. This assumes calls are pretty consistent throughout the half hour – actual average from the data would be different. This table includes abandoned calls, which should be included in the total number of calls

    I would be very hesitant to make any changes to the system based on this level of data. About the only decision I would trust from this level of detail is to get more detailed information.

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    #190662

    Akbar
    Participant

    Hi there,
    I also have a similar query! I want to come out with Standard Time for a particular process. I have already collected data over a period of time considering all types of variations.

    Please advice, if it is a good idea to go by ‘Mean’ in graphical summary when data is normal. I am also getting skewed data, flat histogram, bi-modal sometimes.

    Is there any standard or guideline existing to arrive on standard time for a given process.

    Awaiting response.

    Thanks,
    Akbar

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    #190664

    French
    Member

    How I would arrive at “standard time” for a process depends on several things, including the problem I’m trying to address, what I intend to do with the information, the distribution of the data and the variability in the data. There is not a single, standard answer.

    Rather than thinking of a process in terms of a single number, you’re better off understanding the distribution of your data.

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