ASTM D6708-01
(Practice)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
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
SCOPE
1.1 This practice defines statistical methodology for assessing 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 requirement 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.
Note 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.
Note 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 (proportional + 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.Note 3--Users are cautioned against applying the cross-method reproducibility 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 measure quantitative (numerical) properties of petroleum or petroleum products.
General Information
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Standards Content (Sample)
An American National Standard
Designation: D 6708 – 01
Standard Practice for
Statistical Assessment and Improvement of the Expected
Agreement Between Two Test Methods that Purport to
1
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope X and Y on identical material, where one of the methods has
been appropriately bias-corrected in accordance with this
1.1 This practice defines statistical methodology for assess-
practice.
ing the expected agreement between two standard test methods
that purport to measure the same property of a material, and
NOTE 3—Users are cautioned against applying the cross-method repro-
deciding if a simple linear bias correction can further improve ducibility as calculated from this practice to materials that are significantly
different in composition from those actually studied, as the ability of this
the expected agreement. It is intended for use with results
practice to detect and address sample-specific biases (see 6.8) is dependent
collected from an interlaboratory study meeting the require-
on the materials selected for the interlaboratory study. When sample-
ment of Practice D 6300 or equivalent (for example,
specific biases are present, the types and ranges of samples may need to
ISO 4259). The interlaboratory study must be conducted on at
be expanded significantly from the minimum of ten as specified in this
least ten materials that span the intersecting scopes of the test
practice in order to obtain a more comprehensive and reliable 95 %
methods, and results must be obtained from at least six
confidence limits for cross method reproducibility that adequately cover
laboratories using each method. the range of sample specific biases for different types of materials.
1.6 This practice is intended for test methods which mea-
NOTE 1—Examples of standard test methods are those developed by
voluntary consensus standards bodies such as ASTM, IP/BSI, DIN, sure quantitative (numerical) properties of petroleum or petro-
AFNOR, CGSB.
leum products.
1.2 The statistical methodology is based on the premise that
2. Referenced Documents
a bias correction will not be needed. In the absence of strong
2.1 ASTM Standards:
statistical evidence that a bias correction would result in better
D 5580 Test Method for Determination of Benzene, Tolu-
agreement between the two methods, a bias correction is not
ene, Ethylbenzene plm-Xylene, o-Xylene, C and Heavier
made. If a bias correction is required, then the parsimony 9
Aromatics and Total Aromatics in Finished Gasoline by
principle is followed whereby a simple correction is to be
2
Gas Chromatography
favored over a more complex one.
D 5769 Test Method for Determination of Benzene, Tolu-
NOTE 2—Failure to adhere to the parsimony principle generally results
ene, and Total Aromatics in Finished Gasoline by Gas
in models that are over-fitted and do not perform well in practice.
2
Chromatography/Mass Spectrometry
1.3 The bias corrections of this practice are limited to a
D 6299 Practice for Applying Statistical Quality Assurance
constant correction, proportional correction or a linear (propor-
Techniques to Evaluate Analytical Measurement System
3
tional + constant) correction.
Performance
1.4 The bias-correction methods of this practice are method
D 6300 Practice for Determination of Precision and Bias
symmetric, in the sense that equivalent corrections are obtained
Data for Use in Test Methods for Petroleum Products and
3
regardless of which method is bias-corrected to match the
Lubricants
4
other.
2.2 ISO Standard
1.5 A methodology is presented for establishing the 95 %
ISO 4259 Petroleum Products—Determination and applica-
confidence limit (designated by this practice as the cross-
tion of precision data in relation to methods of test.
method reproducibility) for the difference between two results
3. Terminology
where each result is obtained by a different operator using
different apparatus and each applying one of the two methods
3.1 Definitions:
1 2
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Annual Book of ASTM Standards, Vol 05.03.
3
Products and Lubricants and is the direct responsibility of Subcommittee D02.94on Annual Book of ASTM Standards, Vol 05.04.
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Quality Assurance and Statistics. Available from American National Standards Institute, 11 W. 42nd St., 13th
Current edition approved Aug. 10, 2001. Published October 2001. floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D 6708
3.1.1 closeness sum of squares (CSS), n—a
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