ASTM D6708-08
(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
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.
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 ( ˆY) for the other test method (method Y).
Note 7—Users are cautioned to ensure that ˆY is within the scope of method Y before its use.
The between methods reproducibility established by this practice can be used to construct an interval around ˆY that would contain the result of test method Y, if it were conducted, with about 95 % confidence.
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.
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 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 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 3—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 D 6708 assessment was performed, before the change in terminology in this standard practice was adopted.
Note 4—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 interl...
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Designation: D6708 − 08 AnAmerican 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 1.5 A methodology is presented for establishing the 95%
confidence limit (designated by this practice as the between
1.1 This practice covers statistical methodology for assess-
methods reproducibility)forthedifferencebetweentworesults
ingtheexpectedagreementbetweentwostandardtestmethods
where each result is obtained by a different operator using
that purport to measure the same property of a material, and
different apparatus and each applying one of the two methods
deciding if a simple linear bias correction can further improve
X and Y on identical material, where one of the methods has
the expected agreement. It is intended for use with results
been appropriately bias-corrected in accordance with this
collected from an interlaboratory study meeting the require-
practice.
mentofPracticeD6300orequivalent(forexample,ISO4259).
The interlaboratory study must be conducted on at least ten
NOTE 3—In earlier versions of this standard practice, the term “cross-
materials that span the intersecting scopes of the test methods,
method reproducibility” was used in place of the term “between methods
andresultsmustbeobtainedfromatleastsixlaboratoriesusing
reproducibility.” The change was made because the “between methods
each method. reproducibility” term is more intuitive and less confusing. It is important
tonotethatthesetwotermsaresynonymousandinterchangeablewithone
NOTE 1—Examples of standard test methods are those developed by
another,especiallyincaseswherethe“cross-methodreproducibility”term
voluntary consensus standards bodies such as ASTM, IP/BSI, DIN,
was subsequently referenced by name in methods where a D6708
AFNOR, CGSB.
assessment was performed, before the change in terminology in this
1.2 Thestatisticalmethodologyisbasedonthepremisethat
standard practice was adopted.
a bias correction will not be needed. In the absence of strong NOTE 4—Users are cautioned against applying the between methods
reproducibility as calculated from this practice to materials that are
statistical evidence that a bias correction would result in better
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
6.8) 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 2—Failure to adhere to the parsimony principle generally results
reliable 95% confidence limits for between methods reproducibility that
in models that are over-fitted and do not perform well in practice.
adequately cover the range of sample specific biases for different types of
1.3 The bias corrections of this practice are limited to a
materials.
constantcorrection,proportionalcorrectionoralinear(propor-
1.6 This practice is intended for test methods which mea-
tional + constant) correction.
sure quantitative (numerical) properties of petroleum or petro-
1.4 The bias-correction methods of this practice are method
leum products.
symmetric,inthesensethatequivalentcorrectionsareobtained
1.7 The statistical methodology outlined in this practice is
regardless of which method is bias-corrected to match the
also applicable for assessing the expected agreement between
other.
anytwotestmethodsthatpurporttomeasurethesameproperty
1
of a material, provided the results are obtained on the same
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
ProductsandLubricantsandisthedirectresponsibilityofSubcommitteeD02.94on
comparison sample set, the standard error associated with each
Coordinating Subcommittee on Quality Assurance and Statistics.
test result is known, the sample set design meets the require-
Current edition approved Dec. 15, 2008. Published February 2009. Originally
ment of this practice, and the statistical degree of freedom of
approved in 2001. Last previous edition approved in 2007 as D6708–07. DOI:
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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.
An American National Standard
Designation:D6708–07 Designation: D 6708 – 08
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
1.1 This practice covers statistical methodology for assessing the expected agreement between two standard test methods that
purporttomeasurethesamepropertyofamaterial,anddecidingifasimplelinearbiascorrectioncanfurtherimprovetheexpected
agreement. It is intended for use with results collected from an interlaboratory study meeting the requirement of Practice D6300
or equivalent (for example, ISO4259). 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 Amethodology is presented for establishing the 95% confidence limit (designated by this practice as the between methods
reproducibility)forthedifferencebetweentworesultswhereeachresultisobtainedbyadifferentoperatorusingdifferentapparatus
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—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 4—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
twotestmethodsthatpurporttomeasurethesamepropertyofamaterial,providedtheresultsareobtainedonthesamecomparison
sampleset,thestandarderrorassociatedwitheachtestresultisknown,thesamplesetdesignmeetstherequirementofthispractice,
and the statistical degree of freedom of the data set exceeds 30.
1.8Software program CompTM Version 1.0.21 (ADJD
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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.
An American National Standard
Designation:D6708–07 Designation: D 6708 – 08
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
1.1 This practice covers statistical methodology for assessing the expected agreement between two standard test methods that
purporttomeasurethesamepropertyofamaterial,anddecidingifasimplelinearbiascorrectioncanfurtherimprovetheexpected
agreement. It is intended for use with results collected from an interlaboratory study meeting the requirement of Practice D6300
or equivalent (for example, ISO4259). 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 Amethodology is presented for establishing the 95% confidence limit (designated by this practice as the between methods
reproducibility)forthedifferencebetweentworesultswhereeachresultisobtainedbyadifferentoperatorusingdifferentapparatus
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—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 4—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
twotestmethodsthatpurporttomeasurethesamepropertyofamaterial,providedtheresultsareobtainedonthesamecomparison
sampleset,thestandarderrorassociatedwitheachtestresultisknown,thesamplesetdesignmeetstherequirementofthispractice,
and the statistical degree of freedom of the data set exceeds 30.
1.8Software program CompTM Version 1.0.21 (ADJD
...
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