Outliers Unusually large or small observations relative to the rest of the data.
Overcontrol An element often introduced into a process by a well- meaning operator or controller who considers any appreciable deviation from the target value as a special cause. In this case, the operator is wrongly viewing common-cause variation as a fault in the process. Overcontrol of a process can actually increase the variability of the process and is viewed as a form of tampering.
Pareto Chart A problem-solving tool that involves ranking all potential problem areas or sources of variation according to their contribution to cost or total variation. Typically, 80% of the effects come from 20% of the possible causes, so efforts are best spent on these “vital few” causes, temporarily ignoring the “trivial many” causes.