Six Sigma Glossary
Process Spread
The range of values which a given process characteristic displays; this particular term most often applies to the range but may also encompass the variance. The spread may be based on a set of data collected at a specific point in time or may reflect the variability across a given amount of time.
Quality Functional Deployment (QFD)
Structured methodology to identify and translate customer needs and wants into technical requirements and measurable features and characteristic. This tool is used to identify Critical to Quality Characteristics (CTQCs).
Random
Selecting a sample so each item in the population has an equal chance of being selected; lack of predictability; without pattern.
Random Cause
A source of variation which is random; a change in the source (“trivial many” variables) will not produce a highly predictable change in the response (dependent variable), e.g., a correlation does not exist; any individual source of variation results in a small amount of variation in the response; cannot be economically eliminated from a process; an inherent natural source of variation.
Random Variation
Variations in data which result from causes which cannot be pinpointed or controlled.
Regression Analysis
A statistical technique for determining the relationship between one response and one or more independent variables.
Robust
The condition or state in which a response parameter exhibits hermetically to external cause of a nonrandom nature; e.g., impervious to perturbing influence.
Rolled Yield
The combined resulting quality level, stated as a percent acceptable, that occurs when several processes known to produce defects at some rate are combined to produce a product. For example, a product that requires 100 steps, each of which produces a yield of 98.78% will produce a rolled yield of 0%, that is, no acceptable products.
Scatter Diagram
A diagram that displays the relationships between two variables.
Sigma
Standard deviation; an empirical measure based on the analysis of random variation in a standard distribution of values; a uniform distance from the mean or average value such that 68.26% of all values are within 1 sigma on either side of the mean, 95.44% are within 2 sigma, 99.73% are within 3 sigma, 99.9% are within 4 sigma and so forth.
Sigma Level
A statistical estimate of the number of defects that any process will produce equivalent to defects per million opportunities for that process.
Six Sigma Qualities
A combination of verified customer requirements reflected in robust designs and matched to the capability of production processes that creates products with fewer then 3.4 defects per million opportunities to make a defect. World-class quality. A collection of tools and techniques for raising quality to worked-class levels.
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