The exact u chart can be obtained using simple adjustments
- 作者：Chen ; Gemai ; Cheng ; Smiley W.
- 关键词：Normal approximation ; Transformation ; Cornish-Fisher expansion
- 刊名：Statistics and Probability Letters
- 出版年：1998
- 期刊代码：56_01677152
- 类别：mt
- 出版时间：March 30, 1998
- 卷：37
- 期：4
- 页码：357-365
- 文件大小：446 K
摘要
The u chart for monitoring λ, the average number of defects per inspection unit, requires λ to be large to have positive lower control limits, and the false alarm probabilities differ considerably from the nominal normal values. Based on nonlinear transformations, some alternative charts, such as the chart, can achieve large improvement over the u chart. We show in this paper that with very simple adjustments to the control limits of the u chart, one can achieve equal or even better improvement while still working on the original scale. In particular, using the very simple adjustments is equivalent to using the exact Poisson distribution to design a chart. Some guidelines for choosing an appropriate chart are given.