A major objective of Six Sigma quality-control programs is to better meet customers needs. One place where companies have applied Six Sigma is to order delivery times. They have directed efforts at reducing both the mean (average) time to delivery and the variance or standard deviation (dispersion) of the delivery times. Customers want to get their products sooner, as reflected in the mean. But they also want assurance that the product will arrive when promised. This requires delivery schedules to have little random variance. 

Consider the following experience with the implementation of Six Sigma at a major manufacturing company. 

Compute the mean and standard deviation of order-delivery time before and after implementation of Six Sigma. (These functions are available in Excel.) From a customer’s perspective, how would you view the results of this application of Six Sigma?

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Order Delivery Times (Days) Before Six Sigma After Six Sigma 22 30 12 20 11 5 13 8 26 19 14 8 16 20 12 24 18 14 21