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- Computing CPK for bimodal data, either large readings or zero (majority)..

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Aug 27, 2016 2:13 AM
(1493 views)

Hi,

I have data points from measurements of a certain defect. The readings are either zero(majority) or high readings.

For example: How do i get the CPK if the USL is 100? Desirable is the zero reading.

60.1 |

76.8 |

76 |

68.3 |

43.9 |

60.3 |

42.8 |

66.1 |

49.4 |

62.1 |

49.8 |

66.5 |

61.2 |

58.8 |

59.1 |

60.3 |

67.2 |

68.5 |

54.6 |

61.0 |

64.2 |

57.7 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

0 |

2 REPLIES

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Aug 28, 2016 9:43 AM
(1434 views)

I suggest that you use the Distribution Platform, to help you determine the best way to calculate the Cp/Cpk. If you startup the Distribution Platform, and then under the red triangle, go to:

Continuous Fit==>All

it will help you determine which distribution best fits your data, and then under that distribution, it will give you the Cp/Cpk.

Jim

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Aug 29, 2016 10:45 AM
(1434 views)

jabenir, There is one fundamental question you have to answer before calculating Capability Indices: Is your process in statistical control? If the process is not in a "reasonable degree of control", then Capability Analysis is meaningless. As Dr. Wheeler says in one of his books: "What can be said for the capability of a process not I statistical control? Not much!"

Other questions that need to be answered BEFORE a Capability Analysis: Is the data you presented in time order? If not, what is the order and what does a Runs Chart and/or Process Behavior Chart look like? Can you determine defect rates for discrete periods of time with rational sub-grouping?

Steve