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  • #40870

    j
    Participant

    Hi,
     
    When having continuous data but with varying sample size for subgroups: which control chart should I use?
     
    thank you
     
    j

    0
    #127710

    sumant
    Member

    You can use X-bar S chart

    0
    #127730

    BTDT
    Participant

    J:X-bar R (for nostalgic reasons) or X-bar S will give you the same result.If you are using Minitab, the option box for ‘subgroups’ can take either a number or subgroup identifier. UCL and LCL limits will be adjusted according to the size of each subgroup.If you use a number, Minitab will group data in groups of ‘n’. You can also specify a text field and the software will group successive data points with the same subgroup identifier. The data points in the same subgroup must be successive. For example, the software would identify three subgroups in the data:2.3 A3.1 A4.5 A2.3 A5.6 B4.8 B4.6 B2.4 A5.5 A5.6 ACAUTION: Many of the Western Electric rules will not be applied to your data, you must perform many of the tests manually. Even though you can select the control tests manually, Minitab will not perform the tests if the subgroup size changes.Cheers, BTDT

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