ASTM_D_6708_-_21.pdf

Designation:D670821An American National StandardStandard Practice forStatistical Assessment and Improvement of ExpectedAgreement Between Two Test Methods that Purport toMeasure the Same Property of a Material1This standard is issued under the fixed designation D6708;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This practice covers statistical methodology for assess-ing the expected agreement between two different standard testmethods that purport to measure the same property of amaterial,and for the purpose of deciding if a simple linear biascorrection can further improve the expected agreement.It isintended for use with results obtained from interlaboratorystudies meeting the requirement of Practice D6300 or equiva-lent(for example,ISO 4259).The interlaboratory studies shallbe conducted on at least ten materials in common that amongthem span the intersecting scopes of the test methods,andresults shall be obtained from at least six laboratories usingeach method.Requirements in this practice shall be met inorder for the assessment to be considered suitable for publica-tion in either method,if such publication includes claim tohave been carried out in compliance with this practice.Anysuch publication shall include mandatory information regard-ing certain details of the assessment outcome as specified in theReport section of this practice.1.2 The statistical methodology is based on the premise thata bias correction will not be needed.In the absence of strongstatistical evidence that a bias correction would result in betteragreement between the two methods,a bias correction is notmade.If a bias correction is required,then the parsimonyprinciple is followed whereby a simple correction is to befavored over a more complex one.NOTE1Failure to adhere to the parsimony principle generally resultsin models that are over-fitted and do not perform well in practice.1.3 The bias corrections of this practice are limited to aconstant correction,proportional correction,or a linear(pro-portional+constant)correction.1.4 The bias-correction methods of this practice are methodsymmetric,in the sense that equivalent corrections are obtainedregardless of which method is bias-corrected to match theother.1.5 Amethodology is presented for establishing the numeri-cal limit(designated by this practice as the between methodsreproducibility)that would be exceeded about 5%of the time(one case in 20 in the long run)for the difference between tworesults where each result is obtained by a different operatorusing different apparatus and each applying one of the twomethods X and Y on identical material,where one of themethods has been appropriately bias-corrected in accordancewith this practice,in the normal and correct operation of bothtest methods.NOTE2In earlier versions of this standard practice,the term“cross-method reproducibility”was used in place of the term“between methodsreproducibility.”The change was made because the“between methodsreproducibility”term is more intuitive and less confusing.It is importantto note that these two terms are synonymous and interchangeable with oneanother,especially in cases where the“cross-method reproducibility”termwas subsequently referenced by name in methods where a D6708assessment was performed,before the change in terminology in thisstandard practice was adopted.NOTE3Users are cautioned against applying the between methodsreproducibility as calculated from this practice to materials that aresignificantly different in composition from those actually studied,as theability of this practice to detect and address sample-specific biases(see6.7)is dependent on the materials selected for the interlaboratory study.When sample-specific biases are present,the types and ranges of samplesmay need to be expanded significantly from the minimum of ten asspecified in this practice in order to obtain a more comprehensive andreliable between methods reproducibility that adequately cover the rangeof sample-specific biases for different types of materials.1.6 This practice is intended for test methods which mea-sure quantitative(numerical)properties of petroleum or petro-leum products.1.7 The statistical calculations of this practice are alsoapplicable for assessing the expected agreement between twodifferent test methods that purport to measure the sameproperty of a material using results that are not as described in1.1,provided the results and associated statistics from each testmethod are obtained from a specifically designed multi-labstudy or from a proficiency testing program(e.g.:ILCP)where1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts,Liquid Fuels,and Lubricants and is the direct responsibility of Subcom-mittee D02.94 on C