The values of the mean, as well as the values of 1, 2 and 3 SDs are needed to develop the. If none of the rules are violated, then the process is deemed “in-control” and the run is accepted. Levey-Jennings control charts and Westgard rules. If any one of the following rules are violated (13s, 22s, R4s, 41s or 10x-bar), then the process is deemed “out-of-control” and the run is rejected. Give suggestions for troubleshooting quality. Provide practical examples of QC in laboratory environments. If one or more samples are outside of 2 standard deviations, then the other rules are evaluated. Detail Westgard rules used to identify QC problems. If both samples are within 2 standard deviations (2s), then the process is deemed “in-control” and the run is accepted. Anytime a single measurement exceeds a 2s control limit, you respond by inspecting the control data using the other rules (shown in white underneath). This test is in yellow, to be used as a warning to trigger application of the other rules. The first decision is whether the samples pass the 12s rule. These could be 2 measurements on one control material or 1 measurement on each of two different control materials. The table below shows the notation using subscripts.Ī decision tree (below) is used to determine if the multiple samples collected when control was done can be released.įor this example, 2 samples are collected (N=2). Short hand notations are used to abbreviate different decision criteria or control rules, such as 12s to indicate 1 control measurement exceeding 2s control limits. The protocol includes the 12-s, 13-s, 22-s, R-4s. The rules are applied to the Levey-Jennings Chart instead of the traditional Shewhart individuals control chart, which uses slightly different calculations for the control limits. Westgard rules: ( westgahrd rlz ) A quality control protocol that allows detection of random and systematic error.

The rules were originally developed by James Westgard. They are based on the Western Electric Rules and Nelson Rules, but are modified for multiple samples in a laboratory setting. The Westgard rules are used for laboratory quality control using “runs” consisting of measurements of multiple samples (typically 2-4 samples), called multi-rule.

Westgard rules examples