May 2026 CPHQ Prep Virtual Class-CPHQ Virtual Live Review Course

CPHQ Virtual Live Review Course | Video: Control Charts Part 1

Video Transcription

Video Summary

A Shewhart control chart plots data in chronological order with a mean centerline and statistically calculated control limits (typically at 3 sigma). Points beyond limits signal unusual variation requiring investigation. Control charts assess process stability and whether variation is common cause (inherent to the system, stable and predictable) or special cause (due to specific circumstances, unstable). If a stable process is unacceptable, redesign is needed (e.g., via PDSA). Special-cause detection uses rules: one point outside limits; 8-point shift; 6-point trend; 2 of 3 points in outer third; and 15 points near the centerline.

Keywords

Shewhart control chart

3-sigma control limits

common cause vs special cause variation

process stability assessment

special-cause detection rules