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Evaluation of Nonnormal Process Capability Indices Using Generalized Lambda Distribution

Summary: [This abstract is based on the author's abstract.]Process capability indices (PCIs) used to describe the ability of a manufacturing process to produce items within specified limits are developed under the assumption that the underlying process distribution is normal. However, in situations where process distribution cannot be described by a normal distribution, these PCIs will give misleading results. A procedure is described using the generalized lambda distribution (GLD) curve to compute generalized PCIs useful for the representation of data when the underlying model is unknown. Necessary formulas are provided for fitting a GLD curve, estimating its parameters, performing goodness-of-fit tests, and computing generalized PCIs.

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  • Topics: Process Capability
  • Keywords: Goodness of fit,Process capability index (Cpk),Nonconformance,Lambda plot
  • Author: Pal, Surajit
  • Journal: Quality Engineering