Other Indications of Special Causes

Trends, runs and non-random patterns, where all the points lie within the control limits, can also indicate the presence of special causes.

Again, the data might point to:

• an out of control situation
• a change in process spread
• a process shift
• a change in the level of process performance

Trends, runs and non-random patterns often provide advance warning of unfavourable conditions. Remember:

• Traditional Quality Control takes action on the output.
• Statistical Process Control takes action on the process.