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

CPHQ Virtual Live Review Course | Video: Control Charts Part 2

Video Transcription

Video Summary

A control chart (Shewhart chart) is a line graph like a run chart but includes a mean (center line) plus upper and lower control limits to distinguish common-cause from special-cause variation. With fewer than 12 points, use a run chart only; at 12 points you can calculate temporary “trial” limits, and after 20–30 points refine them. Once a process is stable, extend the center line and limits into the future rather than recalculating each time, so true signals aren’t masked. Control charts detect statistically significant change, support monitoring, identify improvement or degradation, and assess whether changes are sustained.

Keywords

Control chart

Shewhart chart

Upper and lower control limits

Common-cause vs special-cause variation

Process stability monitoring