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Showing Improvement On A Control Chart

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  • #43726

    Schuette
    Participant

    Which control chart (I Chart, Time Series, etc) is the best to use when displaying the results of an improvement. Also, how do you display when the improvement was made compared to how the process was performing prior to the improvement…….Thanks…. 

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    #139131

    Heebeegeebee BB
    Participant

    I prefer comparing Baseline and post-improvement Capability Six Pack’s (Minitab).
     

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    #139133

    Lorax
    Participant

    You could do a hyp test comparing the before and after situations to prove the difference is real or not. Then to highlight the step change, recalculate the average, UCL and LCL at the point when the alteration to the process would have taken effect.
    Lorax
     

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    #139422

    Alastair Lea
    Participant

    The choice of chart is dependant on the item being measured.
    Once the chart is running, check the output for out of control conditions. Out of control in the correct direction is an improvement.
    If the process shifts beyond the UCL or LCL and stays in the NEW favorable position. This is hypothesis testing on the fly and demonstrates that the process has changed.
    Then recalculate a new UCL and LCL.
    The key is to identify the item in the process that was changed to result in the new improved output.

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    #139430

    MB
    Participant

    Jim,
    As the othere guys have said the relevant chart to use is dependant on the type of data you have but a good way of showing your before (as is) and after (to be) is (providing you have minitab) as follows:
    On your minitab file have a seperate column which indicates when the data was collected ie “as is” and “to be” this will allow you to seperate the control chart by this column later
    Select the chart you want to use (stat/control chart ..?….)
    Select Chart Options
    Select Stages
    In the define stages area select the column you have just set up
    Click ok….ok.
     
    This chart should now be split into “as is” and “to be”
     
     
    Hope this helps!?
     
    MB

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    #139434

    WigWam
    Member

    Hi Jim,
    I agree with the method described by MB. I have just used such an I-MR chart to demonstrate phased change with the separator column having Before, During and After. With the UCL Mean and X-bar calculated on the after the visual change can be quite dramatic for a gate review, especially if it s overlaid with a time line showing the DMAIC milestones and change implementation dates. 
    WW

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