首先，你必須確定這些數(shù)據(jù)是否為這個(gè)小組或者個(gè)體樣品計(jì)算所提供的手段。如果它們?yōu)閭�(gè)體樣品(我猜測(cè)這個(gè)正是你們?cè)谡務(wù)摰那樾?，這些數(shù)據(jù)的標(biāo)準(zhǔn)偏差在允許的范圍內(nèi)被估計(jì)，其和數(shù)據(jù)的序列有關(guān)系。所以，如果你改變數(shù)據(jù)的序列，你將會(huì)得到不同的標(biāo)準(zhǔn)偏差。同時(shí)，如此不同的 CPK會(huì)給不同的規(guī)格提供修正。

　　Second， you have to understand thoroughly what Cpk is all about. It‘s a process capability ratiCpk=min{Cpl，Cpu}. It shows how well the process is centered on the target comparing with Cp. So generally people use Cp and Cpk togather trying to figure out the process capability. Furthermore， there are cases where process capability is low but the process is in control，and there are cases where the process is out of control but the process capability is comparative high. These are all related to the variance of the process and how well the process is targeted. There are lots of misleadings in the use of the process capability ratios in the industries.

　　CP其次，你必須全面理解什么是CPK. 它是一個(gè)加工能力比率Cpk=min{Cpl，Cpu}，其顯示出該能力是目標(biāo)中心并優(yōu)于CP.因此，人們通常將CP和CPK一起使用，并嘗試?yán)斫馄浼庸つ芰�。此外，這里有很多情形就是加工能力低但加工處于控制之中，而加工處于控制之外時(shí)加工能力則相對(duì)較高。他們與加工的方方面面聯(lián)系，同時(shí)加工有很強(qiáng)的目的性。在工業(yè)CP中使用加工能力的過(guò)程中出現(xiàn)了許多誤導(dǎo)的情形。

　　In some industries， such as auto industry， people call the calculation of Cpk as Ppk. As to why people use 32 or more data to calculate Cpk， I did a little research about it. In the industry，people accept Cp 1.33 as a commom sense for existing process which corresponds to 4 sigma variance level. If you use this date to do a little calculatiuon and check the table published by Quality Society of America( I was trying to post that table before， but it didn‘t work. It was all messy. I guess the admin deleted that post)， you will get the number approximately 32. But even 32 is not enough sometimes to get a unbiased estimation of the process capability ratio.