Six Sigma SPC - Statistical Process Control

Six Sigma SPC's Quality Control Dictionary and Glossary
2070 W. Washington St. #5 Springfield IL 62702  Ph: 217.698.0063
6 Sigma Statistical Process Control (SPC) Software for Windows 95/98/NT/2000/XP/ME


Home Search Capability Studies Links

Click Here!

Prices FAQ
About Support
Contact Quality Control Dictionary and Glossary Free Desktop 6 Sigma Calculator Forum
Quality Books Articles Free Online 6 Sigma Calculator Free Newsletter

Z Score

Sometimes also called Z-ratio or Z-value, it is an example of what is called a 'Standard Score'. Z-scores are typically associated with a normal distribution, and the interpretation is based on a standard normal look up table. Z-scores are restricted to distributions that approximate a normal distribution. Non-normal distributions could be changed into Z-scores however. When this is done, a standard normal table cannot be used, due to the fact that the shapes of the Z-Score distributions in the table are designed for a normal distribution.

A conversion, it represents the distance in sigma of a given sample from the population's mean, sometimes referred to as X-Bar.

The formula for computing Z-Score is:

(X - Population Mean)
Z = ----------------------------

Where, X is the mean, Population Mean is X-Bar, and sigma is standard deviation.

The resulting Z value is looked up in a table to find a probability of obtaining a value equal to or less than X.

Back to the Quality Control Dictionary and Glossary

Click Here!

Copyright � 2005 Six Sigma SPC / Jim Winings All Rights Reserved
Privacy Statement - Disclaimer - Copyright - Site Map

Last Updated: Wednesday, 07-Jun-06 19:34:41 PDT