ASTM D6708-21

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
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Designation: D6708 − 19a D6708 − 21 An American National Standard
Standard Practice for
Statistical Assessment and Improvement of 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 D6708; 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.
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ε NOTE—Editorially updated Fig. 1 in October 2020.
1. Scope*
1.1 This practice covers statistical methodology for assessing the expected agreement between two different standard test methods
that purport to measure the same property of a material, and for the purpose of deciding if a simple linear bias correction can further
improve the expected agreement. It is intended for use with results obtained from interlaboratory studies meeting the requirement
of Practice D6300 or equivalent (for example, ISO 4259). The interlaboratory studies shall be conducted on at least ten materials
in common that among them span the intersecting scopes of the test methods, and results shall be obtained from at least six
laboratories using each method. Requirements in this practice shall be met in order for the assessment to be considered suitable
for publication in either method, if such publication includes claim to have been carried out in compliance with this practice. Any
such publication shall include mandatory information regarding certain details of the assessment outcome as specified in the Report
section of this practice.
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 1—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 numerical limit (designated by this practice as the between methods
reproducibility) that would be exceeded about 5 % of the time (one case in 20 in the long run) 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
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This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.94 on Coordinating Subcommittee on Quality Assurance and Statistics.
Current edition approved Nov. 1, 2019May 1, 2021. Published November 2019May 2021. Originally approved in 2001. Last previous edition approved in 2019 as
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D6708 – 19.D6708 – 19a . DOI: 10.1520/D6708-19AE01.10.1520/D6708-21.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D6708 − 21
Y on identical material, where one of the methods has been appropriately bias-corrected in accordance with this practice, in the
normal and correct operation of both test methods.
NOTE 2—In earlier versions of this standard practice, the term “cross-method reproducibility” was used in place of the term “between methods
reproducibility.” The change was made because the “between methods reproducibility” term is more intuitive and less confusing. It is important to note
that these two terms are synonymous and interchangeable with one another, especially in cases where the “cross-method reproducibility” term was
subsequently referenced by name in methods where a D6708 assessment was performed, before the change in terminology in this standard practice was
adopted.
NOTE 3—Users are cautioned against applying the between methods reproducibilit
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6708 − 21 An American National Standard
Standard Practice for
Statistical Assessment and Improvement of 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 D6708; 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* 1.4 The bias-correction methods of this practice are method
symmetric, in the sense that equivalent corrections are obtained
1.1 This practice covers statistical methodology for assess-
regardless of which method is bias-corrected to match the
ing the expected agreement between two different standard test
other.
methods that purport to measure the same property of a
1.5 A methodology is presented for establishing the numeri-
material, and for the purpose of deciding if a simple linear bias
cal limit (designated by this practice as the between methods
correction can further improve the expected agreement. It is
reproducibility) that would be exceeded about 5 % of the time
intended for use with results obtained from interlaboratory
(one case in 20 in the long run) for the difference between two
studies meeting the requirement of Practice D6300 or equiva-
results where each result is obtained by a different operator
lent (for example, ISO 4259). The interlaboratory studies shall
using different apparatus and each applying one of the two
be conducted on at least ten materials in common that among
methods X and Y on identical material, where one of the
them span the intersecting scopes of the test methods, and
methods has been appropriately bias-corrected in accordance
results shall be obtained from at least six laboratories using
with this practice, in the normal and correct operation of both
each method. Requirements in this practice shall be met in
test methods.
order for the assessment to be considered suitable for publica-
NOTE 2—In earlier versions of this standard practice, the term “cross-
tion in either method, if such publication includes claim to
method reproducibility” was used in place of the term “between methods
have been carried out in compliance with this practice. Any
reproducibility.” The change was made because the “between methods
such publication shall include mandatory information regard-
reproducibility” term is more intuitive and less confusing. It is important
to note that these two terms are synonymous and interchangeable with one
ing certain details of the assessment outcome as specified in the
another, especially in cases where the “cross-method reproducibility” term
Report section of this practice.
was subsequently referenced by name in methods where a D6708
assessment was performed, before the change in terminology in this
1.2 The statistical methodology is based on the premise that
standard practice was adopted.
a bias correction will not be needed. In the absence of strong
NOTE 3—Users are cautioned against applying the between methods
statistical evidence that a bias correction would result in better
reproducibility as calculated from this practice to materials that are
agreement between the two methods, a bias correction is not significantly different in composition from those actually studied, as the
ability of this practice to detect and address sample-specific biases (see
made. If a bias correction is required, then the parsimony
6.7) is dependent on the materials selected for the interlaboratory study.
principle is followed whereby a simple correction is to be
When sample-specific biases are present, the types and ranges of samples
favored over a more complex one.
may need to be expanded significantly from the minimum of ten as
specified in this practice in order to obtain a more comprehensive and
NOTE 1—Failure to adhere to the parsimony principle generally results
reliable between methods reproducibility that adequately cover the range
in models that are over-fitted and do not perform well in practice.
of sample-specific biases for different types of materials.
1.6 This practice is intended for test methods which mea-
1.3 The bias corrections of this practice are limited to a
sure quantitative (numerical) properties of petroleum or petro-
constant correction, proportional correction, or a linear (pro-
leum products.
portional + constant) correction.
1.7 The statistical calculations of this practice are also
applicable for assessing the expected agreement between two
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different test methods that purport to measure the same
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubrica
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