In Six Sigma methodology, the term “sigma” is used to indicate the extent to which a process varies from its expected performance. In this context, sigma primarily refers to _______

In statistics, sigma (σ) denotes the standard deviation, which measures how much process outcomes deviate from the mean. In Six Sigma, it is the statistical measure of dispersion representing the standard deviation, which quantifies how much process data varies or spreads around the process mean (average). It is used to express process variability and assess the process’s capability to produce outputs within specified limits. A process operating at a higher sigma level (like 6 sigma) has its specifications (limits) far away from the mean in terms of standard deviations, resulting in far fewer defects with 6 sigma being the goal for near-perfect quality (only 3.4 errors per million process events). Sigma Levels & Quality: • 1 Sigma: ~30% yield, ~697,612 defects per million opportunities. • 3 Sigma: ~93.32% yield, ~66,810 defects per million opportunities. • 6 Sigma: ~99.9997% yield, 3.4 defects per million opportunities (near perfection).