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Chapter 13
G. Measurement System Analysis
Define and describe various elements,
including identifying and measuring bias,
stability, accuracy, linearity, etc., and
reviewing repeatability and reproducibility
(R&R) studies. (Comprehension)
Part II.G
Body of Knowledge II.G
In this chapter we discuss measurement system analysis (MSA). MSA is used to
understand and quantify the variability associated with measurements and measurement
systems. It should be noted that a discussion of MSA should come after
the mastery of the statistical content provided in Chapter 18, Basic Statistics and
Applications. MSA is being discussed prior to the discussion of basic statistics
and applications in this book to preserve the order of topics as presented in the
Certified Quality Inspector Body of Knowledge.
The Automotive Industry Action Group (AIAG) reference manual on MSA
(3rd edition) defines measurement as “. . . the assignment of numbers [or values]
to material things to represent the relations among them with respect to particular
properties” (Eisenhart 1963). Similarly, the AIAG reference manual on MSA
(3rd edition) defines a measurement system as “. . . the collection of instruments
or gages, standards, operations, methods, fixtures, software, personnel, environment,
and assumptions used to quantify a unit of measure or fix assessment to the
feature characteristic being measured; the complete process used to obtain measurements”
(Eisenhart 1963).
These definitions will serve as the basis of our discussion. However, before we
begin that discussion we first must provide a clarification. The term MSA is commonly
used interchangeably with the term gage repeatability and reproducibility
(GR&R). MSA is actually a more comprehensive analysis quantifying variability
components from gage stability, gage bias, gage linearity, gage repeatability, and
reproducibility (that is, variability from operator measurements). Gage repeatability
and reproducibility is, in fact, a subset or component of MSA. The reason
underlying the mistaken interchange of the terms MSA and GR&R is that many,
if not most, problems with measurement systems are detected and corrected with
GR&R procedures without having to continue the more comprehensive analysis
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