This week’s blog concludes our series on process capability and asks which is better: Cpk or Ppk?

Your supplier has sent you the process capability chart you requested. Looks like your supplier is really performing for you. You note that his process has a Ppk = 1.14 and a Cpk = 2.07. Why are those different? Well, it doesn’t matter. The Cpk is above 1.33, which is what you asked the supplier for. You just missed a very important piece of information about your supplier’s performance. Know what it is?

You hear the term process capability a lot these days. Customers want to know your process capability. You want to know your supplier’s process capability. So, what is meant by the words process capability? For a process:

Process capability is the range of values that you can expect to get from the process over an extended time period.