The Average
Run Length is the number of points that,
on average, will be plotted on a control
chart before an out of control
condition is indicated (for example a point
plotting outside the control limits).
If the process is in control:
If the process is out of control:
Where α
is the probability of a Type I error and
β
the
probability of a Type II error.
For an overview of this topic see the Statistical
Process Control entry.
