In statistical quality control, the regression control chart allows for monitoring a change in a process where two or more variables are correlated. The change in a dependent variable can be detected and compensatory change in the independent variable can be recommended.
Regression control chart differs from a traditional control chart in four main aspects:
- It is designed to control a varying (rather than a constant) average.
- The control limit lines are parallel to the regression line rather than the horizontal line.
- The computations here are much more complex.
- It is appropriate for use in more complex situations.
The general idea of the regression control chart is as follows: Suppose one is monitoring the relationship between the number of parts produced and the number of work hours expended. Within reasonable limits, on may expect that the greater the number of work hours, the more parts are produced. One could randomly draw 5 sample work days from each month, and monitor that relationship. The control limits established in the regression control chart will allow one to detect, when the relationship changes, for example, when productivity drops and more work hours are necessary to produce the same number of parts.