May 2026 CPHQ Prep Virtual Class-Run chart Rules and Control Chart rules

Run chart Rules and Control Chart rules

Pdf Summary

The document explains basic <strong>run chart</strong> and <strong>control chart</strong> rules used to detect special cause variation in data.

For <strong>run charts</strong>, four main rules are listed:

1. <strong>Shift</strong>: A shift occurs when there are <strong>six or more consecutive points</strong> all above or all below the center line. Points exactly on the center line are ignored and do not count toward or break a shift.

2. <strong>Trend</strong>: A trend occurs when there are <strong>five or more consecutive points</strong> all moving upward or all moving downward. If two or more points have the same value, only the first is counted; repeated equal values do not affect the trend.

3. <strong>Too many or too few runs</strong>: A run is a sequence of points on the same side of the center line. An unusual number of runs, meaning too many or too few crossings of the center line, suggests a nonrandom pattern. To count a new run, the data must actually cross the center line.

4. <strong>Astronomical data point</strong>: This is a point that is clearly different from the others and universally recognized as unusual. Not every highest or lowest point is astronomical.

For <strong>control charts</strong>, five special cause rules are given:

1. <strong>Single point outside control limits</strong>
2. <strong>Shift</strong>: <strong>Eight or more consecutive points</strong> above or below the center line
3. <strong>Trend</strong>: <strong>Six or more consecutive points</strong> steadily increasing or decreasing
4. <strong>2 of 3 points in the outer one-third</strong> of the chart near a control limit
5. <strong>15 or more points in the inner one-third</strong> of the chart near the center line

Overall, the document describes how to identify patterns in charts that may indicate special cause variation rather than random fluctuation.

Keywords

run chart

control chart

special cause variation

shift

trend

runs

center line

control limits

astronomical data point

nonrandom pattern