Process Tampering (aka overcontrol) is a false attempt made by stable process’s managers who try to make unnecessary adjustments to this process aiming to compensate for results which fall within the expected range of variability (common cause variation). Process Tampering occurs when people try to respond the normal variation in a process as if this process was shifted (went wrong): as if the variation in results was produced by emergent causes, not by the common ones, hence the tampering activities can be called “responding to false alarm”.
Consequences of tampering attempt can be even worse than if managers had left this process untouched: a proportion of the output which is out of specification limits can increase. To avoid tampering it is necessary for process managers to study statistics of the process and to utilize the control charts to review the natural control limits defined by common cause variation. If the managers intrude into the process without statistical thinking and profound ideas on its improvement, they risk increasing the variation of the process and reducing its manageability.