June 2001

Vol. 3, No. 6

Quality Quiz
from Dr. Cleary

You're right!

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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