Statistical Process Control Glossary
Control
The process of monitoring and regulating the stability, variation and predictability of a process using statistical tools.
Control Chart
SPC tool that monitors variance in a process over time that may lead to defects.
CTQ (Critical to Quality)
Element of a process that has a direct bearing on quality.
Dashboard
A set of metrics that provide a summary of Six Sigma project status.
Deviation
The difference between the actual value and the desired value for a variable in a process.
DFSS (Design for Six Sigma)
A systematic methodology that uses statistical tools and software to to design products and processes that meet customer expectations.
Distribution
The tendency of a variable's value to group around a central value with a certain amount of "spread" on either side of the value.
DMAIC (Define, Measure, Analyze, Improve and Control)
A process for continued improvement used in statistical process control for Six Sigma.
Pareto Diagram
Focuses on problems with the greatest potential for improvement. Based on the Pareto Principle that states that 20% of sources cause 80% of problems.
Root Cause Analysis
An analysis of the the source reason for a defect or non-conformance for a process.
Sigma Level
A value from 1 to 6 that signifies the maximum number of defects per million:
1 Sigma = 690,000 defects/million
2 Sigma = 308,537 defects/million
3 Sigma = 66,807 defects/million
4 Sigma = 6,210 defects/million
5 Sigma = 233 defects/million
6 Sixma = 3.4 defects/million
Six Sigma
A measure of quality that mandates a maximum of 3.4 defects per million opportunities (DPMO) for a process, product or service transaction.
Standard Deviation
A statistical measure of variance that describes the "spread".
Statistical Control
A condition that describes a process free from non-random or "special cause" variation.
Statistical Process Control (SPC)
The application of statistical methods to control a process.
Statistical Quality Control (SQC)
Often used interchangeably with statistical quality control, SQC includes acceptance sampling in addition to statistical process control.
Variance
A change in a process that can alter its expected outcome.
Z-Score
Sometimes called a standard score, the Z-score how a process deviates from the distribution mean, expressed in units of standard deviation.
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