Trend Limits

Ques:  Solutions to CAPA data: 

Ans:    Re: problem of the expanding 3 sigma limits as complaints increase; the only approach I have used when this problem surfaces, is to have SOP defined steps to react to the absolute number of complaints (if of a high risk nature) rather than the Alert (1.96-2 sigma) and Action (3.0 sigma) limits; e.g.,  a "may cause death" problem requires a resolution to that specific event, not to a trend. The Alert / Action limits will only trigger action if there's a major bolus of a category of complaints in one month.

Oues:  Other process capability tools other than Cpk:

Ans:  The Control Chart, or % defective; or range of SD (standard deviations) of a key dimension; or the reverse of the Cpk, the Zmax3e:  3 sigma limit of tail of distribution / curve furthest  from the specation mid point (or:  Cpk = Zmin/3), where Cpk is the 3 sigma limit of the tail of the distribution / curve closest to the specification mid point); I've never seen this used.