菲尔-扎罗罗伯特，工艺表征的行业标准是 Cpk，有时是 Cpu；拉斯基博士已经讨论过这个问题，因为它与装配工艺有关。关于材料，有时正态分布并不成立。我们该怎么办？
Robert Ploessl: Excellent question. Process engineers love Cpk, because it's a single number that encapsulates process capability. However, when you deal with materials, especially impurities in those materials, you have to be aware of a couple of things. The material, the compound, that we manufacture is not manufactured to hit a certain impurity level. The impurity is not really a product performance specification that we're trying to manufacture to. An impurity is, of course, something that you're trying to get rid of.
菲尔-扎罗 对
Robert Ploessl：没有下限是最好的。你要控制的是上层，也就是 Cpu 部分的 "u"。
菲尔-扎罗 对
Robert Ploessl：除此之外，杂质的分布通常是非正态分布。它通常偏向高端。除此之外，数据集的左端也会发生一些情况，因为你所使用的检测技术总是有一个检测极限。检测极限会带来统计学家所说的 "数据删减"，因此你要处理的是左删减数据。
例如，您有一个数据集，上面写着我们针对铁这样的杂质进行了测量。我们的检测限小于 1ppm。从你的生产线上生产出一批又一批产品，在其中一些产品中，你会测量到小于 1ppm 的杂质，因为这是检测极限。
菲尔-扎罗对
Robert Ploessl: If you then think about the distribution of your data set, that left-censoring now will make the distribution look decidedly non-normal. You will have this large bar at the left end, and you will have some kind of distribution above that. You can't just calculate a mean and a standard deviation, and plug it into the Cpk or Cpu formula, and expect that that value will really make sense.
Sometimes, we need to educate customers on the effects of this distribution on this value. Sometimes, of course, we deal with customers; they have excellent process engineers that are well-educated in these problems.
菲尔-扎罗对
Robert Ploessl：我们非常非常愿意与客户合作，共同研究数据集，制定合理的流程能力指标。当然，这些指标始终取决于客户的具体要求。没有 "一刀切 "的做法。这就是客户的声音，客户的声音会与我们流程的声音相匹配；当然，它们必须协同工作。
菲尔-扎罗没错，正如你所说，这可能会给客户带来真正的窘境。你建议他们怎么做？
Robert Ploessl: Dialogue and conversation. We love it when customers approach us about these specific issues. It's always best to start the conversation in person on these issues. Customers are always welcome to contact us via email or call me. Of course, our website, indiumstg.wpenginepowered.com has a treasure of data and papers on process control issues by Dr. Ron Lasky. I would invite anybody to read the many, many papers he's written on these issues and understand process capability better.
菲尔-扎罗罗伯特，非常感谢。
罗伯特-普洛斯尔：不客气。
菲尔-扎罗我很荣幸
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