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Westgard Rules for Levey Jennings Charts

Labs Running Control Charts Use Westgard Rules

Westgard Rules are used with Levey Jennings Charts in laboratories. They use a slightly different subset of traditional rules with a couple of special rules.

Westgard Rules are Included in QI Macros Excel Add-in

westgard control chart rules

Westgard Rules

Like traditional control chart rules, Westgard rules include Western Electric rules 1, 2, 4 and Nelson's Rule 5.

1. One point above UCL or below LCL (1_3s)
2. Two points above/below 2 sigma (2_2s)
4. Eight points in a row above/below the center line (8_x), note: this rule will catch 9-12_x
5. A trend of seven points in a row increasing or decreasing (7_t)

The uncommon Westgard rule is number 9: Four points above/below 1 sigma (4_1s)or two points in a row with one above and one below 2 sigma (_R4s).

QI Macros Control Charts Turn Unstable Points/ Conditions Red

control chart stability analysis rules

QI Macros control charts also turn the markers for unstable points into diamonds instead of squares.

This helps to identify unstable points and trends when printing control charts on a black and white printer.

control chart with unstable points highlighted

How to Change to Westgard Rules in QI Macros

QI Macros use Montgomery's Rules as the default. However, you can easily switch to the Westgard Rules using the QI Macros menu. See How to Change Control Chart Rules in QI Macros.