common cause

Seeking the Causes of Variation

Not all variation is created equal. Planned variation, like that in an experiment, is a process improvement strategy. Unplanned variation, however, is nearly always bad. Two types of variation concern a Six Sigma team: Common cause variation – All processes have common cause variation. This variation, also known as noise, is a normal part of…


Remember Common Cause Variation in Fight Against Waste

Ideally, practitioners want an error rate to be at 0 percent. But if an error rate is steadily hovering at about 2 percent, it is fair to say that the errors are due to common cause variation. If the error rate suddenly surges beyond its usual level, however, it is probably due to some change…