Tim,
I appreciate your e-mail. However, I am not the expert. The experts are those in the forums so I will defer to them to debate.
No - I must admit, I interpret Cpk and Ppk as defined earlier in this thread. I know six sigma enthusiasts claim quite a lot. Six sigma its self has been debated rather severely in the forums (see
Six Sigma - Statistical Tools - Valid or Hype? Value? Can a CQE do the same? ) as to whether it's Motion Lotion that works or totally over hyped sales indoctrination.
I must admit that I believe a lot of the Six Sigma is sales. I was privileged to be trusted by the Motorola Semi-Conductor Sector (or what was) with internal documents (the old 'You tell and we shoot you') and my impression was, and is, that this is nothing more than understanding statistics and using data to manage. From one document:
In early 1987 the concept and goal of Six Sigma capability was introduced.
There was nothing really 'secret' in the documents, but rather techniques and theories.
My background was biology with chemistry and anthropology as minors in college. I dealt with processes on the level of atomic / molecular reactions. So when I got into 'product' manufacturing I was amazed at how few companies used statistics to manage their processes. In biology I saw the Cause and Effect thing up close. Root Cause in manufacturing, which few really understand, was part and parcel of a biological system and understanding failure modes at the molecular level. This was particularly helpful to me when I had to work in micro-electronics where the cause of a component failure was often an upstream component 'event' - hard to diagnose. Bottom line is we're talking complex systems.
Cpk and Ppk are essentially unitless numbers used to indicate whether a process is 'in control' or not using distribution, location and probability as a base.
I would very much appreciate your discussion on this in the forums. You state:
Why and how this has happened is a long explanation.
We would all really like to hear the long version. The more specifics the better.
With respect to your Excel spreadsheet offer, I can bet over 500 downloads if you post it as an attachment (Which means you agree that it is acceptable per, as a minimum, the constraints as defined at:
https://www.opensource.org/licenses/gpl-license.php ). Or, if it too large to attach to your post, send it to me as an e-mail attachment and I'll put it in the 'Free Files' (
Free Fils directory ) for you.
There is no doubt in my mind that your contributions - both your reasoned, detailed explanation of how and why Cpk and Ppk definitions have switched due to Six Sigma - and your gracious offer to share your spreadsheet - will be appreciated by folks around the world!
My Regards and My Thanks!
Marc T. Smith
