Two Improved Runs Rules for the Shewhart X¯ Control Chart

Runs rules are incorporated into the Shewhart X¯ control chart to increase its sensitivity in detecting small process shifts so that assignable causes can be detected more quickly. In this article, two improved runs rules are suggested. Average run length values for these new improved rules are computed and compared with that of the existing ones. The comparison shows that the new improved rules are superior in performance for large process average shifts, while maintaining the same sensitivity in the detection of small shifts.