Impact of the Measurement System on Process Capability

When a process is not capable, most organizations start to scramble to improve the process. But it could be that the process is fine and it is the measurement system variation that is leading us to think we have a poor process. We could be wasting time trying to reduce the process variation when the first thing we should be working on is the measurement system.

When the percentage of the total variation that the measurement system takes up is very low (such as 20%), we don’t see much of an impact on the process capability. But once the measurement system starts to take up a great deal of the total variation, then our view of our capability is seriously distorted by the impact of the measurement system variation. We could have a capable process, but get a capability number that indicates it is not.