Applying rules to a Shewhart control chart

Apply advanced rules to increase the sensitivity of a Shewhart control chart to detect small shifts, drift, and other patterns.

  1. Activate the analysis report worksheet.
  2. On the Analyse-it ribbon tab, in the Process Control group, click Apply Rules, and then click:
    Option Description
    Standard Apply the standard action rule only.
    WECO Apply the original 4 rules defined by the Western Electric CO.
    Nelson Apply the 8 rules suggested by Lloyd S. Nelson.
    Montgomery Apply the 8 Nelson rules as modified by Douglas C. Montgomery.
    Custom Apply a user-defined set of rules.
    The analysis task pane Control Chart (Shewhart) panel opens.
  3. Optional: To customize which rules to apply, select or clear the check boxes alongside the rules.
  4. Optional: To change either or both the Run length, and Sigma in a custom ruleset, type the new value in the edit box(es) alongside the rules.
  5. Optional: To standardize the quality characteristic statistic, so the control limits are constant regardless of the size of each subgroup, select the Standardized plot check box.
  6. Optional: To show ±1,2,3 sigma zones for interpreting rules, select the Zones check box.
  7. Click Recalculate.
A red asterisk marks points on the control chart that break a rule. A label indicates the broken rule number. Line segments between the points that form part of the broken rule are colored orange.
Note: Rule numbering depends on the ruleset applied. Only rule 1 is the same regardless of the ruleset.