Laboratories need to determine the sigma quality of their tests and methods if they are to manage the testing process properly. Statistical Quality Control (SQC) is an essential tool for managing analytical quality, but the rules and number of control measurements should be optimized for quality and efficiency. It is very easy to figure out the right SQC by using Westgard Sigma Rules™!

The hard part is defining how good a test needs to be for its intended clinical use (e.g., the allowable Total Error, TEa), determining the precision (SD, CV) from a replication experiment or from routine SQC data, and determining accuracy (bias) from a comparison of methods experiment or from periodic proficiency testing results.

After calculation of sigma quality, the Westgard Sigma Rules diagram makes it easy to select the right control rules and the right number of control measurements.

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Westgard Sigma Rules

This double-sided poster is available in electronically in PDF format.

To learn more about the Westgard Sigma Rules, visit the Westgard QC, Inc. website at

Additional resources

Learn more about Thermo Scientific™ MAS™ Quality Controls and our LabLink xL Quality Assurance Software.  

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