4:1s, when is it violated under different types of Westgard Rules? - Blog - Westgard QC

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4:1s, when is it violated under different types of Westgard Rules?

The Westgard Rules, in the classic 1981 multirule paper, require a 1:2s violation before other rejection rules are violated.  If you had4 values past 1s, but nothing past 2s, it wouldn't be checked. Under more "modern" Westgard Rules, with the 1:2s warning rule abolished, you don't need to wait until the 2s limit line is violated before interpreting the rule. Under Westgard Sigma Rules, it's further simplified: you don't need to interpret the 4:1s unless the method is 4 Sigma or lower. In other words, for a method of 5 or 6 Sigma quality, neither of the situations below would be considered a rejection-worthy event.

The 4:1s rule for the "classic" Westgard multirule
A 4:1s violation under a modern Westgard multirule
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Thursday, 26 March 2026

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