Six Sigma Statistical Terms
RANDOMNESS
A condition in which any individual event in a set of events has the same mathematical probability of occurrence as all other events within the specified set, i.e., individual events are not predictable even though they may collectively belong to a definable distribution.
RANDOM SAMPLE
One or more samples randomly selected from the universe (population).
RANDOM SAMPLE
Selecting a sample such that each item in the population has an equal chance of being selected; lack of predictability; without pattern.
RANDOM VARIABLE
A variable which can assume any value from a distribution which represents a set of possible values.
RANDOM VARIATIONS
Variations in data which result from causes which cannot be pinpointed or controlled.
RANGE
The difference between the highest and lowest values in a “subgroup” sample.
RANK
Values assigned to items in a sample to determine their relative occurrence in a population.
RATIONAL SUBGROUP
A subgroup is usually made up of consecutive pieces chosen from the process stream so that the variation represented within each subgroup is as small as feasible. Any changes, shifts and drifts in the process will appear as differences between the subgroups, selected over time.
REGRESSION
A statistical technique for determining the best mathematical expression that describes the functional relationship between one response and one or more independent variables.
REJECT REGION
The region of values for which the alternate hypothesis is accepted.
REPLICATION
Repeat observations made under identical test conditions.
REPRESENTATIVE SAMPLE
A sample which accurately reflects a specific condition or set of conditions within the universe.
RESEARCH
Critical and exhaustive investigation or experimentation having for its aim the revision of accepted conclusions in the light of newly discovered facts.
RESIDUAL ERROR See EXPERIMENTAL ERROR.
RESPONSE SURFACE
A graphical (pictorial) analysis technique used in METHODOLOGY (RSM) conjunction with DOE for determining optimum process parameter settings.
ROBUST The condition or state in which a response parameter exhibits a high degree of resistance to external causes of a nonrandom nature; i.e., impervious to perturbing influence.
ROLLED THROUGHPUT YIELD
The product (series multiplication) of all of the individual (RTY) first pass yields of each step of the total process.
ROOT SUM SQUARED (RSS)
Square root of the sum of the squares. Means of combining standard deviations from independent causes.
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