What is Six Sigma?

The Six Sigma methodology is a disciplined approach for improving business performance. It is a measure of quality that strives for near perfection in the execution of a process. To achieve Six Sigma quality, a process must produce no more than 3.4 defects per million opportunities. An opportunity is defined as a chance for non-conformance with (that is, not meeting) the required specifications. This means a key process must be nearly flawless in its execution to achieve Six Sigma quality.

Concept	Meaning
Defect	A failure to meet a business rule (that is, a rule violation).
Process Capability	A sigma value or percentage that reflects the number of times the process was measured without defects divided by the total number of times it was measured. The process sigma graph on the Six Sigma Summary page shows current and historical process capability.
Variation	The stability of a process. A stable process is one with minimal variation. The process sigma graph on the Six Sigma Summary page shows current and historical variations in process performance, as well as trends. A process with little variation and a high sigma value on this graph indicates a stable process.
Critical to Quality	Attributes identified to be most important to the customer. The Pareto charts on the Six Sigma Summary page identify six areas that are critical to the success of a business process.
The Pareto Principle (also known as the 80:20 rule)	A principle that states the majority of defects (80 percent) are caused by a few (20 percent) vital components. The Pareto charts on the Six Sigma Summary page highlight this principle by identifying the components that are responsible for most of the rule violations.
Root Cause	The underlying cause of a defect. Addressing the root cause rather than its symptoms will prevent defects from recurring.