请教：Cpk置信区间
Cpk是通过抽取样本测量进行计算的，即然均值，标准差都有置信度，置信区间的问题，CpK也不应该漏些这些才对？通过样本计算出来的CpK=1.33,中心无偏移 能保证总体不良率就是0.27%吗？即然是抽样，肯定有抽样误差，怎么不考虑了，至少要给出一个下置信限吧！！
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alfawei (威望:22) (江苏 南京) 机械制造 其它 - 质量相关吹牛打屁
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Confidence intervals and bounds
Cp (1 - a) 100% confidence intervals for Cp are
c2a,n = The a percentile of the chi-square distribution with n degrees of freedomn = The degrees of freedom Depending on the method used to estimate s2within, n varies. For,· Pooled standard deviation, n = S (ni - 1), where ni is the ith subgroup size.
Rbar, n = 0.9 k (n - 1), where k is the number of samples and n is the average sample size (S ni / k). · Sbar, n = fn k (n - 1), where k is the number of samples, n is the average sample size (S ni / k), and fn is the adjustment factor that varies with n. Use the table below to get a value for fn.n fn
2 0.88
3 0.92
4 0.94
5 0.95
6, 7 0.96
8, 9 0.97
10-17 0.98
18-64 0.99
65- 1.00
· Average and median moving range, n = k - Rspan + 1, where Rspan is the number of observations used to calculate the moving range and k is the number of samples.· Square root of MSSD, n = k - 1, where k is the number of samples.