iSixSigma

P-chart

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  • #49871

    Van Loon
    Participant

    Hi
    Is tracking % reruns in a process best done with a P-chart ?
    Jan

    0
    #171243

    mcleod
    Member

    P chart is used for constant and/or non-constant sample size defectives
    NP chart is used for constant sample size defectives
    C chart is used for constant sample size defects
    U chart is used for constant and/or non-constant sample size defects
    So, to answer your question, you must answer two questions: 1)are you dealing with defects or defectives? and 2) do yu have constant sample sizes or not?
    The answers to these questions should tell you which chart to use
     

    0
    #171260

    Van Loon
    Participant

    non-constant sample size, defectives.
    How many parts did we produce today, how many where defective.
     
    Jan

    0
    #171266

    Murat Radmard
    Participant

    Hi Jan,
    I would like to give a practical example for this, which set my mind at ease on this subject when I first heard this example.
    Think about a car production company. A PDI department (Pre delivery Inspection) checks for cars before they send to customer.
    Here, defective can be a scratch on the door or break on the front glass, which do not prevent car to perform its own work (to carry something/someone).
    Defect is something like a fatal error on its engine, which hinders car to perform its own work.
    Then for PDI department :
    Use C Chart for defects control for 100 car for every day. (constant production)
    Use U Chart for defects control for changing sample size (variable production, 100 for one day, 50 for another)
    Use NP chart for defectives control for 100 car for everyday.(constant production)
    Use P chart for defectives control for changing sample size (variable production, 100 for one day, 50 for another)
    Hope to be good for you..
    Murat Radmard

    0
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