Statistical Process Control (SPC) charts offer users the chance to monitor the very
heartbeat of their processes. By collecting data they can predict performance. Taking
sample readings from a process seems straightforward. Of does it? Look more
closely. Do we understand our process fully?
In manufacturing areas we probably do. In non-manufacturing areas we may be less
confident. And who collects the data? What sample size is required? How often are
samples taken? These are vital questions to those intending to daily use the control
chart with a view to improving process performance, particularly in nonmanufacturing,
or service, areas where the techniques are new.
The control chart has been with us since 1924. It has been tried and proven, and
accepted as a highly effective tool in improving processes. In view of the fact that
there is currently renewed interest in Shewhart's work, it is important to consider
how the control limits were originally set up.
However, at the end of the day, it is the logic and rules of collecting data and
interpreting the pattern of points on the chart that is the important issue in
understanding process behaviour and the discovery of insights for process
improvement.