Standard Practice for
Statistical Assessment and Improvement of the Expected Agreement Between Two Test Methods that Purport to Measure the Same Property of a Material:
This standard is issued under the fixed designation D 6708;the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice defines statistical methodology for assess-
ing the expected agreement between two standard test methods
that purport to measure the same property of a material, and
deciding if a simple linear bias correction can further improve
the expected agreement. It is intended for use with results
collected from an interlaboratory study meeting the require-
ment of Practice D 6300 or equivalent (for example,
ISO 4259). The interlaboratory study must be conducted on at
least ten materials that span the intersecting scopes of the test
methods, and results must be obtained from at least six
laboratories using each method.
N
OTE
1—Examples of standard test methods are those developed by
voluntary consensus standards bodies such as ASTM, IP/BSI, DIN,
AFNOR, CGSB.
1.2 The statistical methodology is based on the premise that
a bias correction will not be needed. In the absence of strong
statistical evidence that a bias correction would result in better
agreement between the two methods, a bias correction is not
made. If a bias correction is required, then the
parsimony
principle
is followed whereby a simple correction is to be
favored over a more complex one.
N
OTE
2—Failure to adhere to the parsimony principle generally results
in models that are over-fitted and do not perform well in practice.
1.3 The bias corrections of this practice are limited to a
constant correction, proportional correction or a linear (propor-
tional + constant) correction.
1.4 The bias-correction methods of this practice are method
symmetric, in the sense that equivalent corrections are obtained
regardless of which method is bias-corrected to match the
other.
1.5 A methodology is presented for establishing the 95 %
confidence limit (designated by this practice as the
cross-
method reproducibility
) for the difference between two results
where each result is obtained by a different operator using
different apparatus and each applying one of the two methods
X
and
Y
on identical material, where one of the methods has
been appropriately bias-corrected in accordance with this
practice.
N
OTE
3—Users are cautioned against applying the cross-method repro-
ducibility as calculated from this practice to materials that are significantly
different in composition from those actually studied, as the ability of this
practice to detect and address sample-specific biases (see 6.8) is dependent
on the materials selected for the interlaboratory study. When sample-
specific biases are present, the types and ranges of samples may need to
be expanded significantly from the minimum of ten as specified in this
practice in order to obtain a more comprehensive and reliable 95 %
confidence limits for cross method reproducibility that adequately cover
the range of sample specific biases for different types of materials.
1.6 This practice is intended for test methods which mea-
sure quantitative (numerical) properties of petroleum or petro-
leum products.
2. Referenced Documents
2.1
ASTM Standards:
D 5580 Test Method for Determination of Benzene, Tolu-
ene, Ethylbenzene plm-Xylene, o-Xylene, C
9
and Heavier
Aromatics and Total Aromatics in Finished Gasoline by
Gas Chromatography
2
D 5769 Test Method for Determination of Benzene, Tolu-
ene, and Total Aromatics in Finished Gasoline by Gas
Chromatography/Mass Spectrometry
2
D 6299 Practice for Applying Statistical Quality Assurance
Techniques to Evaluate Analytical Measurement System
Performance
2
D 6300 Practice for Determination of Precision and Bias
Data for Use in Test Methods for Petroleum Products and
Lubricants
2
2.2
ISO Standard
3
ISO 4259 Petroleum Products—Determination and applica-
tion of precision data in relation to methods of test.
1
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum
Products and Lubricants and is the direct responsibility of Subcommittee D02.94 on
Quality Assurance and Statistics.
Current edition approved Aug. 10, 2001. Published October 2001
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