Statistical Process Control ( SPC ) is an established quantitative technique for monitoring stable processes. It has built-in, rule driven, predictive functionality that is useful for identifying out of control process characteristics. This is crucial in key market areas such as safety-critical environments e.g. nuclear, oil & gas, and pharmaceuticals.
SPC involves separating Common Cause and Special Cause variation:
- Common Cause variation: is natural and inherent within the process and occurs with every data point (or part being measured). Before assessing the process capability, the variation must be Common Cause variation.
- Special Cause variation: is usually identified by points lying outside the upper control limit and lower control limit. However, there are many cases where points may lie within the control limits and still represent Special Cause variation. These can be indicated by occurrences such as trends and extreme fluctuations.
In making improvements to the process, we should only seek to respond to Special Cause variations. Using this technique, Blue Stream Consulting can help clients identify only the variations in product flow that require action.
