I am from biology background but would want to know what is difference between process capability and process capability index. What are their area of applications. Please clarify me.

]]>what is the Ppk for process have a spread 24 and average 68 and upper limit 82 and lower limit 54

– 1.68

– 2

– 4

– 4.42 ]]>

Jeremy,

I believe you are mistaken. Sigma ^ does indicate estimation, but s denotes sample standard deviation and not population standard deviation. Also, Ppk does not use population standard deviation. It simply uses sample standard deviation. Sigma ^ is correct for both Cp and Pp indices because both are estimated – just using different techniques as discussed by the article.

Nevertheless, there are some oddities about the formulae:

1. Mu needs a hat – or write it as x-bar. Even though you could do this stuff with populations, why would you want to?

2. S-bar / C4 may be one way to estimate std dev using within subgroup deviations, yet R-Bar/d2 I believe is more common.

]]>Wow, improper formulas for both Pp AND Ppk. Get it together.

]]>(USL – LSL)/ 3s, where the real formula is (USL – LSL)/ 6s

]]>How to calculate Cp with Control Chart esp. Attribute Control Chart?? ]]>