Run Charts and Control Charts in Excel
The Evolution of Time Series Analysis From Run Charts to Control Charts
First there were Line Graphs:
Then came Run Charts with an average or median center line:
Then came Control Charts
- The earliest version of the control chart is the line graph showing defects or delay.
- The next version, a run chart, included a line showing the average or median of all values.
- The next version, added upper and lower control limits calculated as +/-3 sigma from the average. Since it was difficult to measure every item produced, sampling was used to reduce the cost of measurement. This reduction, however, led to many different formulas to handle the various sample sizes.
- The latest versions include 1- and 2-sigma lines to facilitate stability analysis, and highlighting to automatically pinpoint potential problems.