ASTM D6708-18
(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 about 95 % confidence.
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 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 D6300 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.
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 95 % confidence limit (designated by this practice as the between methods 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 2: In...
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Designation: D6708 − 18 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* X and Y on identical material, where one of the methods has
been appropriately bias-corrected in accordance with this
1.1 This practice covers statistical methodology for assess-
practice.
ingtheexpectedagreementbetweentwostandardtestmethods
that purport to measure the same property of a material, and
NOTE 2—In earlier versions of this standard practice, the term “cross-
deciding if a simple linear bias correction can further improve
method reproducibility” was used in place of the term “between methods
the expected agreement. It is intended for use with results
reproducibility.” The change was made because the “between methods
collected from an interlaboratory study meeting the require- reproducibility” term is more intuitive and less confusing. It is important
tonotethatthesetwotermsaresynonymousandinterchangeablewithone
mentofPracticeD6300orequivalent(forexample,ISO4259).
another,especiallyincaseswherethe“cross-methodreproducibility”term
The interlaboratory study must be conducted on at least ten
was subsequently referenced by name in methods where a D6708
materials that span the intersecting scopes of the test methods,
assessment was performed, before the change in terminology in this
andresultsmustbeobtainedfromatleastsixlaboratoriesusing
standard practice was adopted.
each method.
NOTE 3—Users are cautioned against applying the between methods
reproducibility as calculated from this practice to materials that are
1.2 The statistical methodology is based on the premise that
significantly different in composition from those actually studied, as the
a bias correction will not be needed. In the absence of strong
ability of this practice to detect and address sample-specific biases (see
statistical evidence that a bias correction would result in better
6.8) is dependent on the materials selected for the interlaboratory study.
agreement between the two methods, a bias correction is not
When sample-specific biases are present, the types and ranges of samples
made. If a bias correction is required, then the parsimony
may need to be expanded significantly from the minimum of ten as
principle is followed whereby a simple correction is to be
specified in this practice in order to obtain a more comprehensive and
favored over a more complex one. reliable 95% confidence limits for between methods reproducibility that
adequately cover the range of sample specific biases for different types of
NOTE 1—Failure to adhere to the parsimony principle generally results
materials.
in models that are over-fitted and do not perform well in practice.
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-
constantcorrection,proportionalcorrectionoralinear(propor-
leum products.
tional + constant) correction.
1.4 The bias-correction methods of this practice are method
1.7 The statistical methodology outlined in this practice is
symmetric,inthesensethatequivalentcorrectionsareobtained
also applicable for assessing the expected agreement between
regardless of which method is bias-corrected to match the
anytwotestmethodsthatpurporttomeasurethesameproperty
other.
of a material, provided the results are obtained on the same
comparison sample set, the standard error associated with each
1.5 A methodology is presented for establishing the 95%
test result is known, and the sample set design meets the
confidence limit (designated by this practice as the between
requirements of this practice, in particular that the statistical
methods reproducibility) for the difference between two results
degree of freedom associated with all standard errors are 30 or
where each result is obtained by a different operator using
different apparatus and each applying one of the two methods greater.
1.8 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom- ization established in the Decision on Principles for the
mittee D02.94 on Coordinating Subcommittee on QualityAssurance and Statistics.
De
...
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 − 16b D6708 − 18 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 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 D6300
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.
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 95 % confidence limit (designated by this practice as the between methods
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 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 6.8) 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
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 petroleum
products.
1.7 The statistical methodology outlined in this practice is also applicable for assessing the expected agreement between any
two test methods that purport to measure the same property of a material, provided the results are obtained on the same comparison
sample set, the standard error associated with each test result is known, and the sample set design meets the requirements of this
practice, in particular that the statistical degree of freedom associated with all standard errors are 30 or greater.
1
This practice is under the jurisdiction of ASTM Committee
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