ASTM D6708-19a
(Practice)Standard Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport to Measure the Same Property of a Material
Standard Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport to Measure the Same Property of a Material
SIGNIFICANCE AND USE
5.1 This practice can be used to determine if a constant, proportional, or linear bias correction can improve the degree of agreement between two methods that purport to measure the same property of a material.
5.2 The bias correction developed in this practice can be applied to a single result (X) obtained from one test method (method X) to obtain a predicted result ( Y^) for the other test method (method Y).
Note 6: Users are cautioned to ensure that Y^ is within the scope of method Y before its use.
5.3 The between methods reproducibility established by this practice can be used to construct an interval around Y^ that would contain the result of test method Y, if it were conducted, with approximately 95 % probability.
5.4 This practice can be used to guide commercial agreements and product disposition decisions involving test methods that have been evaluated relative to each other in accordance with this practice.
5.5 The magnitude of a statistically detectable bias is directly related to the uncertainties of the statistics from the experimental study. These uncertainties are related to both the size of the data set and the precision of the processes being studied. A large data set, or, highly precise test method(s), or both, can reduce the uncertainties of experimental statistics to the point where the “statistically detectable” bias can become “trivially small,” or be considered of no practical consequence in the intended use of the test method under study. Therefore, users of this practice are advised to determine in advance as to the magnitude of bias correction below which they would consider it to be unnecessary, or, of no practical concern for the intended application prior to execution of this practice.
Note 7: It should be noted that the determination of this minimum bias of no practical concern is not a statistical decision, but rather, a subjective decision that is directly dependent on the application requirements of the users.
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 othe...
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Designation: D6708 − 19a 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.Anumber 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,inthesensethatequivalentcorrectionsareobtained
1.1 This practice covers statistical methodology for assess-
regardless of which method is bias-corrected to match the
ingtheexpectedagreementbetweentwodifferentstandardtest
other.
methods that purport to measure the same property of a
1.5 Amethodologyispresentedforestablishingthenumeri-
material,andforthepurposeofdecidingifasimplelinearbias
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, ISO4259). 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
tonotethatthesetwotermsaresynonymousandinterchangeablewithone
ingcertaindetailsoftheassessmentoutcomeasspecifiedinthe
another,especiallyincaseswherethe“cross-methodreproducibility”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
significantly different in composition from those actually studied, as the
agreement between the two methods, a bias correction is not
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.
1.3 The bias corrections of this practice are limited to a 1.6 This practice is intended for test methods which mea-
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
1
different test methods that purport to measure the same
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
property of a material using
...
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.
Designation: D6708 − 19 D6708 − 19a 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*
1.1 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 collectedobtained from an interlaboratory
studystudies meeting the requirement of Practice D6300 or equivalent (for example, ISO 4259). The interlaboratory study
muststudies shall be conducted on at least ten materials that in common that among them span the intersecting scopes of the test
methods, and results mustshall 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
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 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 6.7) 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 between methods 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 petrol
...
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