| Summary: | 碩士 === 國立交通大學 === 統計學研究所 === 98 === Process capability indices have been proposed in the manufacturing industry to prove numerical measures on process reproduction capability, which are effective tools for quality assurance and guidance for process improvement. Motorola, Inc. introduced its Six Sigma quality initiative to the world in the 1980s. Some quality practitioners questioned why the Six Sigma advocates claim it is necessary to add a 1.5σ shift to the process mean when estimating process capability. Bothe (2002) provides a statistical reason for including such a shift in the process average that is base on the chart’s subgroup size. Data in Bothe’ study was assumed to be approximately normally distributed, but the process output is usually not from approximately normally. Some research is about the PCIs adjustment for process output has a non-normal distribution. This paper investigates the average run length of non-normal distribution, non-central chi-squared distribution, and calculate the mean shift adjustments and addresses this problem computing reliable estimates for capability index Cpk for non-central chi-squared process when the statistically adjustments is considered. For illustration purpose, an application example is presented.
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