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What Is Cpk in Laymans Terms
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Posted by: Ajit
Posted on: Thursday, 10th May 2001, 12:00 AM.
Niel / LPM,
The explanation given by Niel is pretty much good, that';s the way one can explain it to a non-statistician.
The only correction is : Cpk measures how close you r to your target and how consistant u r to around your avaerage performance. A person may be performing with minimum variation, but he can be away from his target towards one of the specification limit, which indicates lower Cpk, whereas Cp will be high. On the other hand, a person may be on average exactly at the target, but the variation in performance is high (but still lower than the tolerance band (i.e. specification interval). In such case also Cpk will be lower, but Cp will be high. Cpk will be higher only when you r meeting the target consistently with minimum variation.
For practical example:
Consider Tiger woods playing a long shot in golf game: (though I'm not familiar with terminology of the game, but I'll try to explain with this game itself).
whenever he takes up teh long shot, the ball lands on the ground, after it's long flight in the air crossing a water barrier), it always lands near to the hole (is that called birdie?) within a radius of say 30cm, whereas the green (smooth surface) around the hole is about a radius of 5m. In such scenario Woods has very high Cpk (may be 6 or more). On the otehr hand, another player's ball lands up away from hole within a circualr area (excluding the hole) of 30cm, and this circle is say 1m away from hole. In such case the other guy has same Cp as that of Woods, but lesser Cpk (may be only 1 or so).
On the other hand in another day, if Woods' ball lands up always within a circle of radius 1m, then his Cpk and as well Cp will be lesser than his ealrier day. Since his region of variability has increased.
Message Thread:  | | Cpk Values by Dmitry Kiskatchi on Thursday, 3rd March 2005 |
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