From the course: Six Sigma: Green Belt
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SPC charts for attributes
- Throughout this chapter, we have discussed SPC charts. The main purpose of SPC charts is to enable process owners to know when to intervene and when to leave the process alone. So, let's take some time now to explore SPC charts for attributes where discrete data is used. There are four types of attribute SPC charts. They are, P-chart, which plots the proportion of defective units, for example, proportion of invoices processed incorrectly. There is also the NP-chart where the number of defective units are plotted, for example, number of invoices processed incorrectly. Next, is the C-chart, which plots the number of defects, for example, number of errors in invoices. And finally the U-chart, which plus the number of defects per unit, for example, number of errors per invoice. Here's an example of a NP chart showing number of rejects. The mean number of rejected items is 12 at the centerline. The process is out of control…
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