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NONPoission Distribution

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Viewing 13 posts - 1 through 13 (of 13 total)
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  • #34597

    littleann
    Participant

    thank Tim, Isabel, Andy ‘s reply to my question about Poission distribution.
    I tried Chi squre test, and get rejected.  and mean and variance are not even closed to  equal.  My data is about nonforminities–defects of product, so they are supposed to distribute  poission.
    Now i just dont know what to do. can i still use c chart or u chart on this data?
     
     

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    #95549

    Anonymous
    Guest

    Littleann,
    I believe that what you really need a physical model. If you can provide me with an email address, I’ll describe a simple experiment from which you can derive a statistical model for %defective, DPU, and DPO; and how to distinguish between random and non random defects.
    Cheers,
    Andy

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    #95553

    Savage
    Participant

    Andy,
    If it’s not too much trouble, I would like to see an example of the model you described.
    Thanks,
    [email protected]

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    #95554

    Dr. Steve W.
    Participant

    If so, it is called over dispersion. There are a lot of text books out there that talks about how to handle overdispersion. Overdispersion is very common situation for sount data.

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    #95555

    Dr. Steve W.
    Participant

    long as your subgroup size is 4 or more. The C chart is a little bit more sensensive to deviation from Poission distribution.

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    #95577

    Anonymous
    Guest

    No problem .. give me a couple of days.

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    #96545

    littleann
    Participant

    Dr. Steve W.
    Thanks. you help a lot.
    If  the variance is much larger than mean, we may use square root of variance instead of square root of mean when we calculate sigma in u chart.
    do you think it is a good idea?

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    #150865

    Anonymous
    Participant

    Dr. Steve,The post is 3 years old, but I would be interested in your opinion of Laney’s P’ and U’ charts to handle overdispersion:Laney, David B., P-Charts and U-Charts Work (But Only Sometimes),  Laney, David B., Improved Control Charts for Attribute Data, Quality Engineering 2002;14:531–7.. 

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    #153770

    Martínez
    Participant

    Have you incorporated the Laney P’ chart? Would like to see how you applied it.
    I was looking into the Laney P’ chart as well. If anyone can suggest a place to get more information, please let me know.

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    #153808

    Anonymous
    Participant

    MBB, Here are some references:Laney, David B., P-Charts and U-Charts Work (But Only Sometimes),  Laney, David B., Improved Control Charts for Attribute Data, Quality Engineering 2002;14:531–7. M A Mohammed and D Laney, Overdispersion in health care performance data: Laney’s approach, Qual. Saf. Health Care 2006;15;383-384. Laney’s P’ and U’ have been implemented in SigmaXL Version 5.1.

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    #153809

    Anonymous
    Participant

    Sorry for the duplicate information.  I did not read my earlier post.
    The health care paper is a good example of use.

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    #153823

    Sigmordial
    Member

    Howdy Dr. Steve,
    Interested in your thoughts relative to the overdispersion Little Anne is encountering and if it is due to a non-homogeneous Poisson process.  If so, could she revisit her subgroup composition in the rational subgrouping sampling strategy to remedy this for her control charts?

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    #153853

    Ken Feldman
    Participant

    Is this the old Dr. Steve formerly of BOA affectionately known as JarJar????

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