Westgard Rules for Levey Jennings Charts

Labs running control charts use Westgard rules

Westgard RulesĀ are used with Levey Jennings Charts in laboratories. They use a combination of traditional rules and some unique rules not used in other rule sets.

What are the Westgard Rules?

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

  1. One point above UCL or below LCL (13s)
  2. Two points above/below 2 sigma (22s)
  3. Eight points in a row above/below the center line (8x), note: this rule will catch 9-12x
  4. A trend of seven points in a row increasing or decreasing (7t)
  5. Four points above/below 1 sigma (41s) or two points in a row with one above and one below 2 sigma (R4s).

Westgard rule #9 is unique and is not included in other control chart rule sets.


Westgard rules and many other rule sets are Included in QI Macros add-in for Excel

westgard control chart rules

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.


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