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Sigma level (σ) Area under the probability density function Process yield Process fallout (in terms of DPMO/PPM) 0.33 1 0.3085375387 30.85% 691462 0.67 2 0.6914624613 69.15% 308538 1.00 3 0.9331927987 93.32% 66807 1.33 4 0.9937903347 99.38% 6209 1.67 5 0.9997673709 99.9767% 232.6 2.00 6 0.9999966023 99.99966%
The process capability is a measurable property of a process to the specification, expressed as a process capability index (e.g., C pk or C pm) or as a process performance index (e.g., P pk or P pm).
The failure rate of a six sigma distribution with the mean shifted 1.5 sigma is not equivalent to the failure rate of a 4.5 sigma process with the mean-centered on zero. [9] This allows for the fact that special causes may result in a deterioration in process performance over time and is designed to prevent underestimation of the defect levels ...
DPMO is stated in opportunities per million units for convenience: processes that are considered highly capable (e.g., processes of Six Sigma quality) are those that experience fewer than 3.4 defects per million opportunities (or services provided).
The Level 4 and Level 5 practices of the Capability Maturity Model Integration use this concept. The application of SPC to non-repetitive, knowledge-intensive processes, such as research and development or systems engineering, has encountered skepticism and remains controversial. [9] [10] [11]
Control charts are graphical plots used in production control to determine whether quality and manufacturing processes are being controlled under stable conditions. (ISO 7870-1) [1] The hourly status is arranged on the graph, and the occurrence of abnormalities is judged based on the presence of data that differs from the conventional trend or deviates from the control limit line.
In general Six Sigma with its DMAIC roadmap focuses on improvement of an existing process or processes. DFSS focuses on the creation of new value with inputs from customers, suppliers and business needs. While traditional Six Sigma may also use those inputs, the focus is again on improvement and not design of some new product or system.
In the social sciences, a result may be considered statistically significant if its confidence level is of the order of a two-sigma effect (95%), while in particle physics and astrophysics, there is a convention of requiring statistical significance of a five-sigma effect (99.99994% confidence) to qualify as a discovery.