Reports show a change in performance, this week versus last week or this month versus last month. Perhaps complaints are up; perhaps production is down. Management seeks an explanation and acts. This is tampering. There is every chance that all they will do is increase variation.
Management should be concerned with improving the system. Performance will vary; it varies because of the system. When management asks for explanations, explanations are provided. Usually something or someone is blamed for the difference in performance. The question that should be addressed is ‘why has the system produced this result?’ It should only be addressed by involving all of the people in all of the processes that affect the result. It is not the fault of something or someone, it is generally the fault of the system.
The first thing to do is to establish whether the problems we are having are predictable. That can only be achieved by plotting them in a capability chart. If they are predictable they can only be eradicated by changing the system.