Six Sigma Overview

What is Six Sigma?

Sigma is a statistical concept that represents the amount of variation present in a process relative to customer requirements or specifications. When a process operates at the six sigma level, the variation is so small that the resulting products and services are 99.9997% defect free.

“Six Sigma” is commonly denoted in several different ways. You might see it written as “6σ,” “6 Sigma,” or “6s.”

In addition to being a statistical measure of variation, the term Six Sigma also refers to a business philosophy of focusing on continuous improvement by understanding customers’ needs, analyzing business processes, and instituting proper measurement methods. Furthermore, it is a methodology that an organization uses to ensure that it is improving its key processes.

While Six Sigma corresponds to being 99.9997% defect free, not all business processes need to attain this high a goal. Companies can also use the Six Sigma methodology to identify which of their key business processes would benefit most from improvement and then focus their improvement efforts there.

Process Capability

To increase your organization’s process-sigma level, you must decrease the amount of variation that occurs.

Having less variation gives you the following benefits:

• Greater predictability in the process.

• Less waste and rework, which lowers costs.

• Products and services that perform better and last longer.

• Happier customers who value you as a supplier.

The simple example below illustrates the concept of Six Sigma. Note that the amount of data in this example is limited, but it serves to describe the concept adequately.

Two companies deliver pizza to your house. You want to determine which one can better meet your needs. You always want your pizza delivered at 6 p.m. but are willing to tolerate a delivery anytime between 5:45 p.m. and 6:15 p.m. In this example, the target is 6 p.m. and the customer specifications are 5:45 p.m. on the low side and 6:15 p.m. on the high side.

You decide to order two pizzas at the same time every night for ten days—one pizza from Company A, and one from Company B. You track the delivery times for ten days and collect the following data:

Dominos Table

As the chart above shows, Company A had two occurrences—on Day 2 and Day 6—of pizza arrival times that were outside of your tolerance window of between 5:45 and 6:15. In Six Sigma terminology, these two occurrences are called defects.



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