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How to calculate improvement percentage for ppm?

Discussion in 'SPC - Statistical Process Control' started by Joanne, Dec 23, 2015.

  1. Joanne

    Joanne New Member

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    I have improved defective rate from 8521ppm to 2203ppm.
    What is the improvement percentage for above?
    How should I calculate?
     
  2. Candi1024

    Candi1024 Well-Known Member

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    Improvement/previous I would assume.

    (8521-2203)/8521 = 74%
     
  3. Bev D

    Bev D Moderator Staff Member

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    the improvement is the change - or decrease - in ppm from the start to the new level. the percentage improvement is then the change divided by the start: (8521-2203)/8521 = .74 = 74% improvement

    of course I can't help but ask if these estimates are based on averages of control charted data to ensure the improvement is solid.
     

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