Talk:Process capability index

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Untitled

I propose to use the example of a runway instead. Everybody can imagen that you would like the pilot to land at the middle of the runway each time. -gr, JVP —Preceding unsigned comment added by 145.36.63.11 (talk) 14:45, 20 January 2011 (UTC)[reply]

I corrected the notation for "variability of the process" to standard deviation to avoid confusion between sigma and sigma squared, variance/variability, and standard deviation. Hyoga 11/26/2007

There is no point in listing an equation if you are not going to define what the variables mean. Namely, what on earth is do USL and LSL stand for? Even sigma should be defined for those who do not know what they are looking at.

Fixed. --mabahj 11:00, 12 July 2006 (UTC)

USP - Upper Specification Limit LSL - Lower specification Limit These are related to statistical process control (SPC). -- Manaf 28 June 2007 (EST)

Table for sigma levels

Either this table, or the table in the wikipedia article with the following link is wrong: http://en.wikipedia.org/wiki/Six_Sigma#Sigma_levels

I am not an expert, so please someone revise it. --59.66.122.148 (talk) 13:08, 9 January 2014 (UTC)[reply]

No, they're correct. For process capability to be valid, the process must be stable, so yields of Φ(sigma level) - Φ(-sigma level) as given in the table (in the article coupled with this talk page) are correct. As the Six Sigma article indicates, the yields presented there represent the worst case deterioration of 1.5σ before a control chart is expected to catch the shift or drift, so yields of Φ(sigma level - 1.5) - Φ(-sigma level - 1.5) (for a shift or drift upward; a shift or drift downward is equivalent—you can do the math) are correct in that article. No action required. -- DanielPenfield (talk) 10:02, 27 January 2014 (UTC)[reply]

Example shown has a std. deviation that seems to not match chart data. Mu hat estimate (98.94) is correct, but estimated chart data std. deviation is ~0.869 (unbiased) or ~0.842 (std. population deviation), not 1.03, as stated.

..unless I am missing something or a different method is used for this? Any comments/clarification very welcomed and appreciated.

165.225.34.90 (talk) 23:09, 5 November 2016 (UTC)[reply]

Confusing

The definitions of Cp, Cpk here are exactly the same as for Pp, Ppk in the article Process performance index. Are they meant to be the same and just used under different conditions (under statistical control, not under statistical control)? Or are they meant to be different? A statement about this is required. — Preceding unsigned comment added by 217.13.68.110 (talk) 06:55, 18 July 2017 (UTC)[reply]