A run chart displays observed data as they evolve over time. Just a basic graph that displays data values in a time order. Can be useful for identifying trends or shifts in process but also allows you to test for randomness in the process.

A run chart can reveal shifts and trends, but not points out of control (A run chart does not have control limits; therefore, it cannot detect out of control conditions.) You can turn a run chart into a control chart by adding upper and lower control limits.

Use it to:

  • track improvements (and determine success)
  • display outputs to look for stability or instability

Run Chart Analysis

(These examples are from the wonderful download Developed by Richard Scoville, PhD. (richard@rscoville.net))

Testing a change

  1. Plot the baseline
  2. Extend the median and begin the test
  3. Continue to plot data following the change
  4. Apply the rules
  5. If there was a signal, re-plot with new median
Testing a change with a run chart
Testing a change with a run chart

Decision Rules

Signals of an effective change:

  • Runs – Are there too many or too few for just common cause variation.
    • A run is a series of consecutive points that all lie on the same side of the line.
    • Ignore the points exactly on the line!
  • Clustering – too few runs.
  • Mixtures – too many runs.
  • Shift – 6 or more consecutive points above or below the median.
    • A general rule of thumb is when seven or eight values are in succession above or below the average of the group, a shift has occurred.
  • Trend – 5 or more consecutive increasing or decreasing points.
    • A basic rule of thumb is when a Run Chart exhibits seven or eight points successively up or down, then a trend is clearly present in the data.
  • Astronomical Point – A dramatically different value.
Run Chart Decision Rules
Run Chart Decision Rules

Run Chart Signals

Counting Runs

Counting Runs

How Many Runs?

Expected Runs Table

Run Chart Videos


Comments (6)

Is there perhaps some SAS code that would create the graph in step 5 above. I see that the SAS support document refers to Shewhart Charts.

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