Vol. 3, No. 6
from Dr. Cleary
You are correct. A capability study involves three sources of information:
specifications, estimated sigma, and process average. Cpk uses these summary
statistics. It does not compare individual data points to the specifications.
For a complete explanation of this solution or to learn more about Cpk, go to http://www.pqsystems.com
to read a paper by SPC project manager Matthew
Savage, "How can Cpk be good with data outside the specifications?"
Copyright 2001 PQ Systems.
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