Process performance measures provide an assessment of processes in which process control may not have been achieved. These measures take into account all observed variation from both common and special causes, whereas traditional process capability measures consider only the inherent, common cause process variation.
Performance measures assess the historical performance of a process. Any prediction from them would be useful only to the extent that the future is expected to resemble the past. To capture total variability in a process, performance measures should be assessed from data collected over long periods of time.
When a process is not in a state of control the process distribution is changing through time. Hence, attempts to determine a specific form of a process distribution would be inappropriate. For this reason, performance measures should not consider distributional shape.
Several measures of process performance may be calculated. In this software the following measures will be generated.
Two additional diagnostic measures are also generated as follows.
Making comparisons among theses measures will highlight process losses and improvement opportunities.
These performance measures may be placed in a stacked bar chart. See Stacked Bar Charts.