Roll goods Cpk's and Ppk's cannot be correctly calculated using historical techniques. The primary reason for this relates to the statistical assumptions used in the majority of these calculations.

These are:

1. Single population over time

2. Normal distribution

3. Stationary mean

4. Samples random and independent

5. Process in statistical control

PJ Associates provides our clients with techniques suitable for continuous process manufactured products so that the Cpk and Ppk numbers calculated are statistically meaningful.