1、Designation: D2777 12Standard 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. In principle, all testmethods are covered by this practice.1.2 Except as specified in 1.4, 1.5, and 1.6, this practicerequires the task group proposing a new test method to carryout a collaborative study from which statements for precision(overall
4、and single-operator standard-deviation estimates) andbias can be developed. This practice provides general guidanceto task groups in planning and conducting such determinationsof precision and bias.1.3 This practice also provides guidance to task groups forconducting limited-scale collaborative stud
5、ies (known as“comparability studies”) for test methods that have beenrevised, when such revision includes substantive modifications.Examples of substantive modifications may include, but are notlimited to, changes in mandatory or allowable instrumentation,reagents, reaction times, etc.1.3.1 Changes
6、to applicable water matrices in the Scope ofa method may constitute a substantive modification under thisprovision. However, recognize that even the original collab-orative study may not have used all the various matrix typesspecified in the methods original Scope.1.3.2 A methods concentration-range
7、 extension that isdeemed to merit additional collaborative testing (even withouta method modification that would otherwise be consideredsubstantive) shall 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 ran
8、ge. 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 revision to a test method includes substan-tive modification shall be determined by consensus of theCommittee.1.4 If a full-scale collaborative study is
9、 not technicallyfeasible, due to the nature of the test method or instability ofsamples, the largest feasible scaled-down collaborative studyshall be conducted to provide the best possible limited basis forestimating the overall and single-operator standard deviations.1.4.1 Examples of acceptable sc
10、aled-down studies are thelocal-area studies conducted by Subcommittee D19.24 onmicrobiological methods because of inherent sample instabil-ity. These 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
11、 samples are not feasible under any circum-stances, a statement of single-operator precision will meet therequirements of this practice. Whenever possible, this state-ment should be developed from data generated by independentmultiple operators, each doing replicate analyses on indepen-dent samples
12、(of a specific matrix type), which generally fallwithin specified concentration ranges (see 7.2.5.2 (3).1.4.3 This practice is not applicable to methodology involv-ing continuous sampling or continuous measurement, or both,of specific constituents and properties.1.4.4 This practice is also not appli
13、cable to open-channelflow measurements.1.5 A collaborative study that satisfied the requirements ofthe version of this practice in force when the study wasconducted will continue to be considered an adequate basis forthe precision-and-bias statement required in each test method.If the study does not
14、 satisfy the current minimum requirementsfor a collaborative study, a statement listing the studysdeficiencies and a reference to this paragraph shall be includedin the precision-and-bias statement as the basis for an exemp-tion from the current requirements.1.6 This paragraph relates to special exe
15、mptions not clearlyacceptable under 1.4 or 1.5. With the approval of CommitteeD19 on the recommendation of the Results Advisor and theTechnical Operations Section of the Executive Subcommitteeof Committee D19, a statement giving a compelling reasonwhy compliance with all or specific points of this p
16、racticecannot 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 a1This practice is under the jurisdiction of ASTM Committee D19 on W
17、ater andis the direct responsibility of Subcommittee D19.02 on Quality Systems, Specifi-cation, and Statistics.Current edition approved June 15, 2012. Published July 2012. Originallyapproved in 1969. Last previous edition approved in 2008 as D2777 08E01. DOI:10.1520/D2777-12.2The boldface numbers in
18、 parentheses refer to the list of standards at the end ofthis practice.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.period not to exceed 5 years. Preliminary Standards mustcontain a minimum of a single-operator precision-and-biass
19、tatement 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 this paragraph shall include the date of approval by
20、Committee 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 (“repeatability”). This statement is valid for fivey
21、ears 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 anumerical measure, (2) test methods yielding a non-nume
22、ricalreport 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 some requirementsunder Sections 1.4 through 1.8, sha
23、ll 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 makeevery effort to retain all the data from their round-r
24、obin 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 WaterD1141 Practice for the Preparation of Substitute
25、 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 for Writing Quality Control Specificationsfor Sta
26、ndard Test Methods for Water AnalysisD5905 Practice for the Preparation of Substitute Wastewa-terD6091 Practice for 99a?%/95a?% Interlaboratory Detec-tion Estimate (IDE) for Analytical Methods with Negli-gible Calibration ErrorD6512 Practice for Interlaboratory Quantitation EstimateE177 Practice for
27、 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 MethodE1169 Practice for Conducting Ruggedness Test
28、s2.2 ASTM Adjuncts:DQCALC Microsoft Excel-based software for the Inter-laboratory Quantitation Estimate (IQE)43. Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice, refer to Terminologies D1129, D4375 and E456, andPractice E177.3.2 Definitions of Terms Specific to This Standar
29、d: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 average value of a test method from the assumed
30、 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 laboratory, na single and completely independentanalytical system with its own specific apparatus, so
31、urce ofreagents, set of internal standard-operating procedures, etc.Different laboratories will differ from each other in all of theseaspects, regardless of how physically or organizationally closethey may be to each other.3.2.5 limited validation study, nin a test method, a vali-dation study that d
32、oes not fulfill all D2777 requirements for afull-scale collaborative study, but that can be used for re-validation of revised methods.3.2.6 operator, nusually the individual analyst withineach laboratory who performs the test method throughout thecollaborative study. However, for complicated test me
33、thods,the operator may be a team of individuals, each performing aspecific function throughout the study.3.2.7 precision, nthe degree of agreement of repeatedmeasurements of the same property, expressed in terms ofdispersion of test results about the arithmetical-mean resultobtained by repetitive te
34、sting of a homogeneous sample underspecified conditions. The precision of a test method is ex-pressed quantitatively as the standard deviation computed fromthe results of a series of controlled determinations.3.2.8 substantive modification, nin a test method, achange (or changes) that is deemed by t
35、he Committee to be ofsuch magnitude that the change might affect the precision-and-bias data published with the original method.4. Summary of Practice4.1 After the task group has assured itself that the testmethod has had all preliminary evaluation work completed, the3For referenced ASTM standards,
36、visit the ASTM website, www.astm.org, 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 adjunc
37、t produced in 2007.D2777 122task 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-up to the Results Advisor for concurrence exceptas specified in 1.4, 1.5, and 1.
38、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 developed. The final precision-and-bias statistics mustbe based on usable data from
39、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 statements included are submitted to the subcommitteevice-chairman, who in turn sends a c
40、opy 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 collaborative study shall be complete before asubcommittee ballot. If the collab
41、orative 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 ASTM Headquarters when the test method is submitted bythe subcommittee chairman a
42、s 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 addition, the appendix shows a sample calculationof precision and bias from real co
43、llaborative-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 any laboratory properlyusing the test method studied. These precision-and-bias
44、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 be able to achieve confident detectionand meet the minimum precision (expressed
45、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 extensivetest can only use representative matrices so that universalapplicability can
46、not 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 of the scope and applicability of the test method as written.6. Preliminary Stu
47、dies6.1 Considerable pilot work on a test method must precedethe determination of its precision and bias (2, 3). This pilotwork should explore such variables as preservation require-ments, reaction time, concentration of reagents, interferences,calibration, and sample size. Potentially significant f
48、actorsmust be investigated and controlled in the written test methodin advance of the collaborative test. Also, disregard of suchfactors may introduce so much variation among operators thatresults are misleading or inconclusive (4) (see 9.3 and 9.4). Aruggedness study conducted in a single laborator
49、y is particu-larly useful for such investigations and should be conducted toprove a test method is ready for interlaboratory testing (seeGuide E1169 for details).6.2 Only after a proposed test method has been tried,proved, and reduced to unequivocal written form should adetermination of its precision and bias be attempted.6.3 If the task group intends to evaluate the method char-acteristics of detection and quantification, Practice D6091(Interlaboratory Detection Estimate) or Standard PracticeD6512 (Interlaboratory Quantitation Estimate), or both, shouldbe evaluated
