Variation caused by something going wrong with the process, producing a faulty output, the root cause fo which can be determined and rectified.
Special-cause variation is characterised by:
* New, unanticipated, emergent or previously neglected phenomena within the system;
* Variation inherently unpredictable, even probabilistically;
* Variation outside the historical experience base; and
* Evidence of some inherent change in the system or our knowledge of it.
Special-cause variation always arrives as a surprise. It is the signal within a system. Examples of special cause variation are:
* Poor adjustment of equipment
* Operator falls asleep
* Faulty controllers
* Machine malfunction
* Computer crashes
* Poor batch of raw material
* Power surges
* Broken part
* Operator absent