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Probability Distribution for Cycle Time

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  • #53617

    Trish G
    Participant

    In dealing with staffing estimates etc I use cycle times for transactions etc. the data is not typically “normal” what is the best distribution to use to predict the expected frequency of transactions that take a certain time?

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    #190896

    broderick
    Participant

    Most time-based data sets are postively skewed due to the fact they are naturally bounded at zero. And you can always consider using the often-discussed methods for non-normality – transformation, subgrouping, non-parametrics, etc. Good luck.

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    #190900

    Schwarz
    Participant

    The time between the successive occurance of events is usually modeled by the exponential distribution. This is due to its close relationship to Poisson processes. See any statistics text book for an explanation of how to calculate event probabilities under it.

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    #190903

    Robson
    Participant

    Try Weibull. It’s used for reliability analysis using interval data and it will fit a distribution for you.

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    #190906

    Trish G
    Participant

    Thanks , i was also looking at the Lognormal distribution..any thoughts on that one

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    #190912

    Andell
    Participant

    First display the data in control chart format. Sometimes “special cause” variation can distort a distribution. If it appears stable, then consider using probability plots with normal and log-normal to start. Weibull can be considered, but log-normal often does the job and it’s easier to work with.

    Minitab has a distribution ID utility under its quality and reliability tools. Just be sure to select a subset of distributions, or you’ll get a mountain of outputs.

    If you have any questions, give me a yell: [email protected]. I would never dream of charging for a 5-minute chat.

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    #190913

    Trish G
    Participant

    Great…I will give that a try, thanks much

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