Six Sigma Statistical Terms
ABSCISSA
The horizontal axis of a graph.
ACCEPTANCE REGION
The region of values for which the null hypothesis is accepted.
ALPHA RISK
The probability of accepting the alternate hypothesis when, in reality, the null hypothesis is true.
ALTERNATE HYPOTHESIS
A tentative explanation which indicates that an event does not follow a chance distribution; a contrast to the null hypothesis.
ANALYSIS OF VARIANCE
A statistical method for evaluating the effect that factors (ANOVA) have on process mean and for evaluating the differences between the means of two or more normal distributions.
ASSIGNABLE CAUSE
A process input variable that can be identified and that contributes in an observable manner to non-random shifts in process mean and /or standard deviation.
ASSIGNABLE VARIATIONS
Variations in data which can be attributed to specific causes.
ATTRIBUTE DATA
Quality data that typically reflects the number of conforming or non-conforming units or the number of nonconformities per unit on a go/no go or accept/ reject basis.
AVERAGE
Sum of all measurements divided by the total number of measurements. Statistic which is used to estimate the population mean. Same as MEAN.
BACKGROUND VARIABLES
Variables which are of no experimental interest and are not held constant. Their effects are often assumed insignificant or negligible, or they are randomized to ensure that contamination of the primary response does not occur. Also referred to as environmental variables and uncontrolled variables.
BENCHMARKING
A process for identification of external best-in-class practices and standards for comparison against internal practices.
BETA RISK
The probability of accepting the null hypothesis when, in reality, the alternate hypothesis is true.
BINOMIAL DISTRIBUTION
A statistical distribution associated with data that is one of two possible states such as Go-No Go or Pass-Fail. It is also the distribution generated by rolling dice.
BLACK BELT
A process improvement project team leader who is trained and certified in Six Sigma methodology and tools and who is responsible for successful project execution.
BLOCKINGVARIABLES
A relatively homogenous set of conditions within which different conditions of the primary variables are compared. Used to ensure that background variables do not contaminate the evaluation of primary variables.
BRAINSTORMING
A team-oriented meeting used in problem solving to develop a list of possible causes that may be linked to an observed effect.
CAPABILITY INDICES
A mathematical calculation used to compare the process variation to a specification. Examples are Cp, Cpk, Pp, PpK, Zst, and Zlt. GE uses Zst & Zlt as the common communication language on process capability.
CAUSALITY
The principle that every change implies the operation of a cause.
CAUSATIVE
Effective as a cause.
CAUSE
That which produces an effect or brings about a change.
CAUSE AND EFFECT (C&E)
One of the seven basic tools for problem solving and is DIAGRAM sometimes referred to as a “fishbone” diagram because of its structure. Spine represents the “effect” and the major legs of the structure are the “cause categories.” The substructure represents the list of potential causes which can induce the “effect.” The 6M’s (man, machine, material, method, measurements and Mother Nature, are sometimes used as cause categories.
C CHARTS
Which display the number of defects per sample. Used where sample size is constant.
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