Westgard rule 에 대해서

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http://www.westgard.com/mltirule.htm

What are the "Westgard rules"?

For convenience, we adopt a short hand notation to abbreviate different decision criteria or control rules, e.g., 1_2s to indicate 1 control measurement exceeding 2s control limits. We prefer to use subscripts to indicate the control limits, but other texts and papers may use somewhat different notation (e.g. 1:2s rather than 1_2s) Combinations of rules are generally indicated by using a "slash" mark (/) between control rules, e.g. 1_3s/2_2s.

The individual rule are defined below. The "thumbnail" graphic next to a rule shows an example of control results that violate that rule. You can click on a graphic to get a larger picture that more clearly illustrates the application of each control rule.

13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit.
12s refers to the control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus/minus 2s. In the original Westgard multirule QC procedure, this rule is used as a warning rule to trigger careful inspection of the control data by the following rejection rules.
22s - reject when 2 consecutive control measurements exceed the same mean plus 2s or the same mean minus 2s control limit.
R4s - reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds the mean minus 2s.
41s - reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus 1s control limit.
10x - reject when 10 consecutive control measurements fall on one side of the mean.
In addition, you will sometimes see some modifications of this last rule to make it fit more easily with Ns of 4:
8x - reject when 8 consecutive control measurements fall on one side of the mean.
12x - reject when 12 consecutive control measurements fall on one side of the mean.

The preceding control rules are usually used with N's of 2 or 4, which means they are appropriate when two different control materials are measured 1 or 2 times per material.