1、Designation: D2777 13Standard Practice forDetermination of Precision and Bias of Applicable TestMethods of Committee D19 on Water1This standard is issued under the fixed designation D2777; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, 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. Scope1.1 This practice establishes uniform standards for estimat-ing and expressing the precision and bias of
3、 applicable testmethods for Committee D19 on Water. Statements of precisionand bias in test methods are required by the Form and Style forASTM Standards, “Section A21. Precision and Bias (Manda-tory).” In principle, all test methods are covered by thispractice.1.2 Except as specified in 1.4, 1.5, an
4、d 1.6, this practicerequires the task group proposing a new test method to carryout a collaborative study from which statements for precision(overall and single-operator standard-deviation estimates) andbias can be developed. This practice provides general guidanceto task groups in planning and cond
5、ucting such determinationsof precision and bias.1.3 This practice also provides guidance to task groups forconducting limited-scale collaborative studies (known as“comparability studies”) for test methods that have beenrevised, when such revision includes substantive modifications.Examples of substa
6、ntive modifications may include, but are notlimited to, changes in mandatory or allowable instrumentation,reagents, reaction times, etc.1.3.1 Changes to applicable water matrices in the Scope ofa method may constitute a substantive modification under thisprovision. However, recognize that even the o
7、riginal collab-orative study may not have used all the various matrix typesspecified in the methods original Scope.1.3.2 A methods concentration-range extension that isdeemed to merit additional collaborative testing (even withouta method modification that would otherwise be consideredsubstantive) s
8、hall require a full collaborative study, as de-scribed in Sections 7.1-7.5, but only at Youden-pair concen-trations representative of the extended range. Note that such acollaborative study could involve as little as a single-sampleYouden-pair study in a single reproducible matrix.1.3.3 Whether a re
9、vision to a test method includes substan-tive modification shall be determined by consensus of theCommittee.1.4 If a full-scale collaborative study is not technicallyfeasible, due to the nature of the test method or instability ofsamples, the largest feasible scaled-down collaborative studyshall be
10、conducted to provide the best possible limited basis forestimating the overall and single-operator standard deviations.1.4.1 Examples of acceptable scaled-down studies are thelocal-area studies conducted by Subcommittee D19.24 onmicrobiological methods because of inherent sample instabil-ity. These
11、studies involve six or more completely independentlocal-area analysts who can begin analysis of uniform samplesat an agreed upon time.1.4.2 If uniform samples are not feasible under anycircumstances, a statement of single-operator precision willmeet the requirements of this practice. Whenever possib
12、le, thisstatement should be developed from data generated by inde-pendent multiple operators, each doing replicate analyses onindependent samples (of a specific matrix type), which gener-ally fall within specified concentration ranges (see 7.2.5.2 (3).1.4.3 This practice is not applicable to methodo
13、logy involv-ing continuous sampling or continuous measurement, or both,of specific constituents and properties.1.4.4 This practice is also not applicable to open-channelflow measurements.1.5 A collaborative study that satisfied the requirements ofthe version of this practice in force when the study
14、wasconducted will continue to be considered an adequate basis forthe precision-and-bias statement required in each test method.If the study does not satisfy the current minimum requirementsfor a collaborative study, a statement listing the studysdeficiencies and a reference to this paragraph shall b
15、e includedin the precision-and-bias statement as the basis for an exemp-tion from the current requirements.1.6 This paragraph relates to special exemptions not clearlyacceptable under 1.4 or 1.5. With the approval of CommitteeD19 on the recommendation of the Results Advisor and theTechnical Operatio
16、ns Section of the Executive Subcommitteeof Committee D19, a statement giving a compelling reasonwhy compliance with all or specific points of this practice1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.02 on Quality Systems
17、,Specification, and Statistics.Current edition approved Jan. 1, 2013. Published February 2013. Originallyapproved in 1969. Last previous edition approved in 2012 as D2777 12. DOI:10.1520/D2777-13.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Unit
18、ed States1cannot be achieved will meet both ASTM requirements (1)2and the related requirements of this practice. In addition,Committee D19, through a Main Committee ballot, mayapprove publication of a “Preliminary” Standard Method for aperiod not to exceed 5 years. Preliminary Standards mustcontain
19、a minimum of a single-operator precision-and-biasstatement and a Quality Control section based on the singleoperator data. Publication of a Preliminary Standard is condi-tional on the approval of a full D2777 collaborative studydesign for the standard. Precision-and-bias statements autho-rized by th
20、is paragraph shall include the date of approval byCommittee D19.1.7 Per Section A21.2.3 of the ASTM Form and StyleManual the committee may delay an interlaboratory study fora new method and include a temporary statement in thePrecision and Bias Section that addresses only single operatorprecision (“
21、repeatability”). This statement is valid for fiveyears from the initial publication date. In this case, a singlelaboratory study shall be conducted in accordance with Section7.6.1.8 In Section 12 this practice shows exemplary precision-and-bias-statement formats for: (1) test methods yielding anumer
22、ical measure, (2) test methods yielding a non-numericalreport of success or failure based on criteria specified in theprocedure, and (3) test methods specifying that procedures inanother ASTM test method are to be used with only insignifi-cant modifications.1.9 All studies, even those exempt from so
23、me requirementsunder Sections 1.4 through 1.8, shall receive approval from theResults Advisor before being conducted (see Section 8) andafter completion (see Section 13).1.10 This practice satisfies the QC requirements of PracticeD5847.1.11 It is the intent of this practice that task groups makeever
24、y effort to retain all the data from their round-robin studies.Values should not be eliminated unless solid evidence exists fortheir exclusion. The Results Advisor should work closely withthe task groups to effect this goal.2. Referenced Documents2.1 ASTM Standards:3D1129 Terminology Relating to Wat
25、erD1141 Practice for the Preparation of Substitute OceanWaterD1193 Specification for Reagent WaterD4375 Practice for Basic Statistics in Committee D19 onWaterD5790 Test Method for Measurement of Purgeable OrganicCompounds in Water by Capillary Column GasChromatography/Mass SpectrometryD5847 Practice
26、 for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD5905 Practice for the Preparation of Substitute WastewaterD6091 Practice for 99a?%/95a?% Interlaboratory Detec-tion Estimate (IDE) for Analytical Methods with Negli-gible Calibration ErrorD6512 Practice for Inter
27、laboratory Quantitation EstimateE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE178 Practice for Dealing With Outlying ObservationsE456 Terminology Relating to Quality and StatisticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Me
28、thodE1169 Practice for Conducting Ruggedness Tests2.2 ASTM Adjuncts:DQCALC Microsoft Excel-based software for the Interlabo-ratory Quantitation Estimate (IQE)43. Terminology3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminologies D1129, D4375 and E456, andPractice E177.3.
29、2 Definitions of Terms Specific to This Standard:3.2.1 accuracy, na measure of the degree of conformityof a single test result generated by a specific procedure to theassumed or accepted true value, and includes both precisionand bias.3.2.2 bias, nthe persistent positive or negative deviationof the
30、average value of a test method from the assumed oraccepted true value.3.2.3 comparability study, na collaborative study thatincorporates side-by-side evaluation of the test method beforeand after a substantive modification to a test method.3.2.4 degrees of freedom, nthe total number of replicatesana
31、lyzed across all laboratories/analysts minus the number oflaboratories/analysts.3.2.5 laboratory, na single and completely independentanalytical system with its own specific apparatus, source ofreagents, set of internal standard-operating procedures, etc.3.2.5.1 DiscussionDifferent laboratories will
32、 differ fromeach other in all of these aspects, regardless of how physicallyor organizationally close they may be to each other.3.2.6 limited validation study, nin a test method, a vali-dation study that does not fulfill all D2777 requirements for afull-scale collaborative study, but that can be use
33、d for re-validation of revised methods.3.2.7 operator, nusually the individual analyst within eachlaboratory who performs the test method throughout thecollaborative study.3.2.7.1 DiscussionHowever, for complicated testmethods, the operator may be a team of individuals, eachperforming a specific fun
34、ction throughout the study.3.2.8 precision, nthe degree of agreement of repeatedmeasurements of the same property, expressed in terms of2The boldface numbers in parentheses refer to the list of standards at the end ofthis practice.3For referenced ASTM standards, visit the ASTM website, www.astm.org,
35、 orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from ASTM International Headquarters. Order Adjunct No.ADJDQ-CALC. Original adjunct produced in 2007.D2777 132dispersio
36、n of test results about the arithmetical-mean resultobtained by repetitive testing of a homogeneous sample underspecified conditions.3.2.8.1 DiscussionThe precision of a test method is ex-pressed quantitatively as the standard deviation computed fromthe results of a series of controlled determinatio
37、ns.3.2.9 substantive modification, nin a test method, achange (or changes) that is deemed by the Committee to be ofsuch magnitude that the change might affect the precision-and-bias data published with the original method.3.3 Acronyms3.3.1 MDL, nmethod detection limit4. Summary of Practice4.1 After
38、the task group has assured itself that the testmethod has had all preliminary evaluation work completed, thetask group should prepare the test-method write-up in finalform. The plan for collaborative study is developed in accor-dance with this practice and submitted along with the test-method write-
39、up to the Results Advisor for concurrence exceptas specified in 1.4, 1.5, and 1.6. Upon receipt of concurrence,the collaborative test is conducted, data analyzed, andprecision-and-bias statements formulated by the task group.Estimates of the lower limits of quantitation and detection mayalso be deve
40、loped. The final precision-and-bias statistics mustbe based on usable data from at least six independent labora-tories. The statements, with backup data including thereported-results summary, the calculations leading up to thestatements, and the test method write-up with precision-and-bias statement
41、s included are submitted to the subcommitteevice-chairman, who in turn sends a copy to the ResultsAdvisorfor concurrence before balloting. This procedure assures hav-ing an acceptable copy of the collaborative-study results tosend toASTM for items on the main-committee ballot. In mostinstances, the
42、collaborative study shall be complete before asubcommittee ballot. If the collaborative study is not complete,the test method may go on the ballot as a provisional testmethod rather than a standard test method. Copies of the testdata, approved calculations, and statistical results shall be filedat A
43、STM Headquarters when the test method is submitted bythe subcommittee chairman as an item for the main-committeeballot.4.1.1 The appendix shows an example of “FormAApproval of Plans for Interlaboratory Testing,” as Fig.X1.1.4.1.2 For examples of data-reporting forms, see AppendixX3, 6.0.4.1.3 In add
44、ition, the appendix shows a sample calculationof precision and bias from real collaborative-test data, therelated table of statistics, and the related precision-and-biasstatement.5. Significance and Use5.1 Following this practice should result in precision-and-bias statements that can be achieved by
45、 any laboratory properlyusing the test method studied. These precision-and-bias state-ments provide the basis for generic limits for use in the QualityControl section of the test method. Optionally, the detectionand quantitation values provide estimates of the level at whichmost laboratories should
46、be able to achieve confident detectionand meet the minimum precision (expressed as relative stan-dard deviation) expected.5.2 The method specifies the matrices for which the testmethod is appropriate. The collaborative test corroborates thewrite-up within the limitations of the test design. An exten
47、sivetest can only use representative matrices so that universalapplicability cannot be implied from the results.5.3 The fundamental assumption of the collaborative studyis that the matrices tested, the concentrations tested, and theparticipating laboratories are a representative and fair evalua-tion
48、 of the scope and applicability of the test method as written.6. Preliminary Studies6.1 Considerable pilot work on a test method must precedethe determination of its precision and bias (2, 3). This pilotwork should explore such variables as preservationrequirements, reaction time, concentration of r
49、eagents,interferences, calibration, and sample size. Potentially signifi-cant factors must be investigated and controlled in the writtentest method in advance of the collaborative test.Also, disregardof such factors may introduce so much variation amongoperators that results are misleading or inconclusive (4) (see9.3 and 9.4). A ruggedness study conducted in a singlelaboratory is particularly useful for such investigations andshould be conducted to prove a test method is ready forinterlaboratory testing (see Guide E1169 for details).6.2 Only after a proposed te
