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process capability for attribute data

Discussion in 'Capability - Process, Machine, Gage …' started by kedar, Mar 23, 2016.

  1. kedar

    kedar Member

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    how to calculate "process capability for attribute data". is excel sheet available?
     
  2. Bev D

    Bev D Moderator Staff Member

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    it depends on what you mean by 'process capability'. I just use a control chart - it shows me what the average defect rate is and the limits of possible defect rates. It is always more insightful to see all of the variation in time series.

    If you mean the dreaded capability index then you can take the defect rate (p) and back calculate the index in EXCEL. it's a simple formula:
    Cpk = Z score / 3 = [NORMSINV(1-p)]/3
     
    Miner and Bob Doering like this.
  3. jacklinjot

    jacklinjot Member

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    Attributes capability measures are taken directly from attributes control charts. No additional calculations are required.
     
  4. RoxaneB

    RoxaneB Moderator Staff Member

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    How are no additional calculations required? Measures become the variables that are used as part of applying the process capability calculation. Or have I misunderstood your post?
     
  5. kedar

    kedar Member

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    is excel sheet available?
     
  6. Bev D

    Bev D Moderator Staff Member

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    For which? the control chart or the formula used to convert the defect rate to a "Cpk index"?
    if it's the latter all you need to do is type the formula =NORMSINV*(1-'p')/3 into the cell you want the value to appear
    if it's a control chart I would suggest you either use readily available software or create your own. The formulas for the p chart are very simple - a simple google search will give you the formulas....
     
    kedar, RoxaneB and Atul Khandekar like this.

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