Reply to Christelli : Implementation of new Westgard Rules suggested by the Westgard Advisor software for five immunological parameters. What Six Sigma, quality control, the analytical Sigma-metric, and Westgard Advisor can and cannot do.

The study of Cristelli attempted to find fault with the rules suggested by Westgard Advisor software, claiming that implementing those rules did not improve the method performance. A fundamental misunderstanding of the utility and purpose of the analytical Sigma-metric and QC rules needs to be clarified.