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Slide 144 of 250
There is a wide range of non-random patterns that require action. When the presence of a special cause is suspected, the following actions should be taken (subject to local instructions).
Check that all calculations and plots have been accurately completed, including those for control limits and means. When using variable charts, check that the pair (x bar, and R bar) are consistent. When satisfied that the data is accurate, act immediately.
Investigate the process operation to determine the cause.
Use tools such as:
Cause and Effect
Your investigation should cover issues such as:
The method and tools for measurement
The staff involved (to identify any training needs
Time series, such as staff changes on particular days of the week
Changes in material
Machine wear and maintenance
Mixed samples from different people or machines
Incorrect data, mistakenly or otherwise
Changes in the environment (humidity etc.)