5-sigma quality requires 3 rules, 1 3s/2 2s/R 4s, with 2 control measurements in each run (N=2, R=1).The notation N=2 R=1 indicates that 2 control measurements are needed in a single run. 6-sigma quality requires only a single control rule, 1 3s, with 2 control measurements in each run one on each level of control).The dashed vertical lines that come up from the Sigma Scale show which rules should be applied based on the sigma quality determined in your laboratory. That scale provides guidance for which rules should be applied based on the sigma quality determined in your laboratory. That is an important distinction, but the most important change is the Sigma-scale at the bottom of the diagram. On first glance, it looks just like the Westgard Rules diagram except there is no 2 SD warning rule. We call this tool “Westgard Sigma RulesTM” to distinguish this approach from the original Westgard Rules.įigure 1 shows the Westgard Sigma Rules for 2 levels of control materials. In our recent book Basic Quality Management Systems, we introduced a new tool that is quicker and easier to use than previous tools. We continue to look for faster and simpler tools that will help laboratories select the right SQC for their own applications. The tools include power function graphs, critical-error graphs, QC Selection Grids, charts of operating specifications ( OPSpecs chart), and the QC Validator and EZ Rules 3 computer programs. This work began many years ago with the development of a computer simulation program that could be used to determine the rejection characteristics of various control rules and different numbers of control measurements. Over time, we have developed a variety of QC design and planning tools to support laboratory efforts to select SQC procedures that are right for their specific intended clinical use and the method performance observed in their laboratory. We have long advocated customizing Statistical QC procedures, such as “Westgard Rules”, to take into account the quality required for the intended use of a test and the imprecision and bias observed for a method. Introducing Westgard Sigma Rules TM James O. This article is exclusively sponsored by LGC Technopath Clinical Diagnostics So what happens when we try to talk about both at the same time? Westgard Sigma Rules We've talked about Westgard Rules for decades, and we've talked about Six Sigma for years.
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