Six Sigma Black Belt Exam Prep

Answer: D - B represents a range of special, unexpected variation.

Key Takeaway: Unlike common variation, special variation is unexpected and not inherent to the process that is to be controlled. For example, if a production cycle with a consistently narrow variation produces half of its regular outputs, then a special variation has occurred. Typically, when special variation is measures, the data points fall above or below the Upper Control Limit and the Lower Control Limit which are 3 standard deviations each from the mean.