# Z benchmark

Z benchmark describes the sigma capability of a process.

Z benchmark indices are an alternative to Cp and Pp indices. They are the definition of the sigma capability of a Six Sigma process.

All of the indices assume a normally distributed process quality characteristic with the parameters specified by the process mean and sigma. The process sigma is either the short-term or long-term sigma estimate.

Index | Description |
---|---|

< LSL | The number of sigma units from the process mean to the lower specification limit. |

> USL | The number of sigma units from the process mean to the upper specification limit. |

< SL > | The number of sigma units from the process to mean to the point if all nonconforming units are put in one tail of the distribution. |

Z shift is the difference between the short-term and long-term indices. The larger the Z shift, the more scope there is to improve the process by eliminating shifts and drifts in the process mean. Some industries define the sigma capability of a process as the long-term Z benchmark + a 1.5 Z shift. Meaning a process with a long-term Z benchmark of 4.5 is quoted as a Six Sigma process. It is best to avoid such rules and directly measure the short-term and long-term Z benchmark capability.

- What is Analyse-it?
- Administrator's Guide
- User's Guide
- Statistical Reference Guide
- Distribution
- Compare groups
- Compare pairs
- Contingency tables
- Correlation and association
- Principal component analysis (PCA)
- Factor analysis (FA)
- Item reliability
- Fit model
- Method comparison
- Measurement systems analysis (MSA)
- Reference interval
- Diagnostic performance
- Control charts
- Process capability
- Capability ratios (Cp/Pp indices)
- Z benchmark
- Nonconforming units
- Estimating process capability
- Pareto analysis
- Study Designs
- Bibliography

Version 5.30

Published 15-Apr-2019