Appendix 1: Glossary of Terms
Glossary of Terms
Assignable Cause
Assignable Variations
Attribute Data
Benchmarking
Capability Indices
Cause
Cause and Effect (C&E)
Diagram
C Charts
Characteristic
Confounding
Continuous Data
Control Chart
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.
Variations in data which can be attributed to specific
causes.
Quality data that typically reflects the number of
conforming or non-conforming units or the number of
non-conformities per unit on a go/no go or
accept/reject basis.
A process for identification of external best-in-class
practices and standards for comparison against
internal practices.
A mathematical calculation used to compare the
process variation to a specification. Examples are Cp,
Cpk, Pp, Ppk, Zst, and Zlt as the common
communication language on process capability.
That which produces an effect or brings about a
change.
One of the seven basic tools for problem solving and
is 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.
Charts which display the number of defects per
sample. Used where sample size is constant.
A definable or measurable feature of a process,
product, or service.
Allowing two or more variables to vary together so that
it is impossible to separate their unique effects.
Data obtained from a measurement system which has
an infinite number of possible outcomes.
A graphical rendition of a characteristic’s performance
across time in relation to its natural limits and central
tendency.
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Control Limits
Control Plan
Control Specifications
Critical to Quality (CTQ)
Characteristic
Defect
Defect Per Million
Opportunities (DPMO)
Degrees of Freedom
Dependent Variable
Design of Experiment
(DOE)
Effect
Experiment
Experimental Error
Apply to both range or standard deviation and
subgroup average (X) portions of process control
charts and are used to determine the state of
statistical control. Control limits are derived
statistically and are not related to engineering
specification limits in any way.
A formal quality document that describes all of the
elements required to control variations in a particular
process or could apply to a complete product or family
of products.
Specification requirements for the product being
manufactured.
A drawing characteristic determined to be important
for variability reduction based on a requirement from
production, engineering, customer application, or
regulatory agency. Can also apply to transactional or
service delivery processes.
Any product characteristic that deviates outside of
specification limits.
Quality metric used in the Six Sigma process and is
calculated by the number of defects observed divided
by the number of opportunities for defects normalized
to 1 million units.
The number of independent measurements available
for estimating a population parameter.
A Response Variable; e.g., y is the depedent or
“Response” variable where Y = f(X1…XN) process
input variables.
A formal, proactive method for documenting the
selected controllable factors and their levels, as well
as establishing blocks, replications and response
variables associated with a planned experiment. It is
the plan for conducting the experiment and evaluating
the results.
That which was produced by a cause.
A test under defined conditions to determine an
unknown effect, to illustrate or verify a known law, or
to establish a hypothesis. See Design of Experiment
(DOE).
Variation in observations made under identical test
conditions. Also called residual error. The amount of
variation which cannot be attributed to the variables
included in the experiment.
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Factors
Failure Mode & Effects
Analysis (FMEA)
First Time Yield
Gage Accuracy
Gage Linearity
Gage Repeatability
Gage Stability
Independent Variable
Interaction
Key Process Input
Variables (KPIV’s)
Lower Control Limit
Mean Time Between
Failures (MTBF)
Independent variables.
Analytical technique focused at problem prevention
thru identification of potential problems. The FMEA is
a proactive tool that is used pragmatically to identify
potential failure modes and their effects, to numerically
rate the combined risk associated with severity,
probability of occurrence and detectability and to
document appropriate plans for prevention. FMEA’s
can be applied to system, (application) and product
design and to manufacturing and non-manufacturing
processes (i.e. services & transactional processes).
Yield that occurs in any process step prior to any
rework that may be required (see Yft Symbology) to
overcome process shortcomings.
The average difference observed between a gage
under evaluation and a master gage when measuring
the same parts over multiple readings.
A measure of gage accuracy variation when evaluated
over the expected operating range.
A measure of the variation observed when a single
operator uses a gage to measure a group of randomly
ordered (but identifiable) parts on a repetitive basis.
A measure of variation observed when a gage is used
to measure the same master over an extended period
of time.
A controlled variable; a variable whose value is
independent of the value of another variable.
The tendency of two or more variables to produce an
effect in combination which neither variable would
produce if acting alone.
The vital few input variables, called “x’s”, (normally 26) that drive 80% of the observed variations in the
process output characteristic (“y”).
A horizontal dotted line plotted on a control chart
which represents the lowest process deviation that
should occur if the process is in control (free from
assignable cause variation).
Average time to failure for a statistically significant
population of product operating in its normal
environment.
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Measurement Systems
Analysis (MSA)
Means of evaluating a continuous or discreet
measurement system to quantify the amount of
variation contributed by the measurement system.
Refer to Automotive Std. (AIAG STD) for details.
Out of Control
Condition which applies to statistical process control
chart where plot points fall outside of the control limits
or fail an established run or trend criteria, all of which
indicated that an assignable cause is present in the
process.
Pareto Diagram
A chart which places common occurrences in rank
order.
P Charts
Charts used to plot percent defectives in a sample
where sample size is variable.
Precision to Tolerance
A ratio used to express the portion of engineering
Ratio (P/T)
specification consumed by the 99% confidence
interval of measurement system repeatability and
reproducibility error. (5.15 standard deviations of R&R
error)
Process
A particular method of doing something, generally
involving a number of steps or operations.
Process Control
See Statistical Process Control.
Process Control Chart
Any of a number of various types of graphs upon
which data are plotted against specific control limits.
Process Map
A detailed step-by-step pictorial sequence of a
process showing process inputs, potential or actual
controllable and uncontrollable sources of variation,
process outputs, cycle time, rework operations, and
inspection points.
Quality Function
QFD is a disciplined matrix methodology used for
Deployment (QFD)
documenting customer wants and needs – “the voice
of the customer” – into operational “requirement”
terms. It is an effective tool for determining critical-toquality characteristics for transactional processes,
services and products.
R Chart
Plot of the difference between the highest and lowest
in a sample. Normally associated with the range
control portion of an X, R chart.
Response Surface
A graphical (pictorial) analysis technique used in
Methodology (RSM)
conjunction with DOE for determining optimum
process parameter settings.
Rolled Throughput Yield The product (series multiplication) of all of the
(RTY)
individual first pass yields of each step of the total
process.
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Short Run Statistical
Process Control
Six M’s
Six Sigma
Special Cause
Stable Process
Standard Deviation
Statistical Control
Statistical Process
Control (SPC)
Upper Control Limit
Variation
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X & R Charts
A statistical control charting technique which applies to
any process situation where there is insufficient
frequency of subgroup data to use traditional control
charts (typically associated with low-volume
manufacturing or where setups occur frequently).
Multiple part numbers and multiple process streams
can be plotted on a single chart.
The major categories that contribute to effects on the
fishbone diagram (man, machine, material, method,
measurement, and mother nature).
A term coined by Motorola to express process
capability in parts per million. A Six Sigma process
generates a maximum defect probability of 3.4 parts
per million (PPM) when the amount of process shifts
and drifts are controlled over the long term to less than
+1.5 standard deviations.
See Assignable Cause.
A process which is free of assignable causes, e.g., in
statistical control.
A statistical index of variability which describes the
process spread or width of distribution.
A quantitative condition which describes a process
that is free of assignable/special causes of variation
(both mean and standard deviation). Such a condition
is most often evidence on a control chart, i.e., a control
chart which displays an absence of nonrandom
variation.
The application of standardized statistical methods
and procedures to a process for control purposes.
A horizontal line on a control chart (usually dotted)
which represents the upper limits of capability for a
process operating with only random variation.
Any quantifiable difference between individual
measurements; such differences can be classified as
being due to common causes (random) or special
causes (assignable).
A control chart which is a representation of process
capability over time; displays the variability in the
process average and range across time.
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