#### Tim Folkerts

**Trusted Information Resource**

**interpreting the common capability indices: Cp, Cpk, Pk, and Ppk.**

Rather than start with a theoretical presentation of the equations, my plan is to

**start with the data**. In subsequent posts, I will present data for a hypothetical process. Each set of data is generated to illustrate one or more specific features. By seeing the data and the capability indices,

**hopefully the interpretation will be more concrete**, more intuitive.

Unless other wise stated, the following will be true of all the data:

- The process has
**specification limits at +/- 5** - Data is generated from a
**normal distribution** - Data are collected into
**subgroups of 4** - Calculations will be based on
**30 subgroups**(occasionally 100 subgroups) - Processing is done with
**Minitab** - Data will be
**screened**; the data is randomly generated, but data sets that are "too unusual" will be discarded in favor of data that more clearly illustrates the desired features.

Comments are, of course, welcome. If there are any particular situations you would like illustrated, let me know, and I can try to work it into the series.

Tim