Six Sigma eLearning Glossary of Six Sigma Terms (N - R)

A - D

E - M

N -R

S - Z

Noise Variable
A nuisance or uncontrolled factor that adds variation to a process or product.

An operation that does not transform the product in a way that is meaningful to the customer and is not needed for operational success.

Null Hypothesis
Statement of no change or difference.  The default is to assume the Null Hypothesis to be true unless refuted by sufficient evidence.  If the Null Hypothesis is refuted, the Alternate Hypothesis is accepted instead, with a certain level of confidence.

Number of Distinct Categories 
Ratio of the standard deviation of the parts to standard deviation of the measurement system.

An experiment strategy that changes one factor at a time to evaluate its effects on an output. An OFAT experimental strategy can be inefficient in terms of requiring more runs than a DOE approach, and can miss interactions and the optimal settings.

An analysis technique for determining whether any mean is significantly different from other means, and for evaluating single factor experiments.

P- & NP-Charts
Control charts for defectives.

Passive Opportunities
Parts + Connections.

A process improvement tool for on-line use in full production.

Poisson Distribution
Probability function that is used for charts for defects.

Fool-proofing, error-proofing, A control method that makes it very unlikely or impossible for an error to occur.

Polynomial Model
A mathematical model or equation in which the response is a described as a function of input factors and input factors raised to integer exponents, such as input factors squared:  Y= b0 + b1 X1 + b2 X1^2 + error.

Population Parameter
Fixed, but unknown characteristics describing the distribution for all values of an entire group.

Population Variance
The average of the squared deviation of each individual data points from the population mean for all values of an entire group.

Positional Variation
Within piece variation.

The probability of detecting a real difference, or 100% minus the Beta risk, the risk of incorrectly concluding that there is no difference.

The distance between the mean and the nearest specification limit divided by (3 x long term standard deviation ).

The total variation due to the measurement system.

A technique of controlling processes that do not run at steady state.

Primary Metric
A gauge used to measure project progress (dpu, RTY, etc.).

Consists of input, value-add, and output.

Process Flow Diagram
A detailed map of every step in the process, including hidden factory steps.

Process Improvement
Successful projects will improve quality, delight the customer, enhance employee development, increase process effectiveness & efficiency, and result in greater corporate profit, and a higher return on investment (ROI).

Project Team
Performs the process improvement tasks.

Process Improvement Methodology
The tactics of Six Sigma methodology.

Pure Error
The variation in the data that is estimated by repeat runs.

Randomized Block Design
An experiment containing two sets of categorical inputs, one set of which consists of noise variable(s).

The numerical distance between the highest and lowest values in a data set.

Red Tagging
A technique used for sorting the necessary from the unnecessary.

Reduced Model
The best-fit predictive equation using only the statistically significant factors and interactions.

Region of Curvature
The region where one or more significant inputs no longer conforms to a linear model.

Regression Equation
A prediction equation which allows values of inputs to be used to predict the value of outputs.

The inherent variability of the measurement device.  The variability of measurements under similar conditions such as the same operator and same measurement device.

Experimental runs using the same combination of treatments, run consecutively without new setups.

The number of times the entire experiment is repeated.  Combinations are not run consecutively.

The variability of a measurement device when measurements are made under different conditions such as with different operators or different measurement devices.

The difference between the expected value from a model and the experimental data value.

Response Surface
The surface of the expected value of an output or response modeled as a function of significant inputs.

Risk Priority Number
An index used in FMEA (Failure Modes and Effects Analysis) to prioritize possible failure conditions, calculated as the product of Severity x Occurrence x Detection Difficulty. If Severity, Probability of Occurrence and Detection difficulty are each evaluated on a 1-10 scale, then the Risk Priority Number can range from 1 to 1000.

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