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2、n American National StandardStandard Practice forDetermination of Precision and Bias of Applicable TestMethods of Committee D19 on Water1This standard is issued under the fixed designation D 2777; the number immediately following the designation indicates the year oforiginal adoption or, in the case
3、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 a
4、nd bias of applicable test methods for Committee D19 on Water.1.2 Except as specified in 1.3, 1.4, and 1.5, this practice requires the task group proposing a new test method to carry out a collaborative study from which statements for precision(overall and single-operator standard-deviation estimate
5、s) and bias can be developed. This practice provides general guidance to task groups in planning and conducting such determinations of precision and bias.1.3 If a full-scale collaborative study is not technically feasible, due to the nature of the test method or instability of samples, the largest f
6、easible scaled-down collaborative study shall be conducted to provide the best possible limited basis for estimating the overall and single-operator standard deviations.1.3.1 Examples of acceptable scaled-down studies are the local-area studies conducted by Subcommittee D19.24 on microbiological met
7、hods because of inherent sample instabil- ity. These studies involve six or more completely independent local-area analysts who can begin analysis of uniform samples at an agreed upon time.1.3.2 If uniform samples are not feasible under any circum- stances, a statement of single-operator precision w
8、ill meet the requirements of this practice. Whenever possible, this state- ment should be developed from data generated by independent multiple operators, each doing replicate analyses on indepen- dent samples (of a specific matrix type), which generally fall within specified concentration ranges (s
9、ee 7.2.5.2( 3).1.3.3 This practice is not applicable to methodology involv- ing continuous sampling or continuous measurement, or both, of specific constituents and properties.1.3.4 This practice is also not applicable to open-channel flow measurements.1 This practice is under the jurisdiction of AS
10、TM Committee D19 on Water and is the direct responsibility of Subcommittee D19.02 on General Specifications,Technical Resources, and Statistical Methods.Current edition approved Aug. 10, 2003. Published September 2003. Originally approved in 1969. Last previous edition approved in 1998 as D 2777 98.
11、1.4 A collaborative study that satisfied the requirements ofthe version of this practice in force when the study was conducted will continue to be considered an adequate basis for the precision-and-bias statement required in each test method.If the study does not satisfy the current minimum requirem
12、ents for a collaborative study, a statement listing the studys deficiencies and a reference to this paragraph shall be included in the precision-and-bias statement as the basis for an exemp- tion from the current requirements.1.5 This paragraph relates to special exemptions not clearly acceptable un
13、der 1.3 or 1.4. With the approval of Committee D19 on the recommendation of the Results Advisor and the Technical Operations Section of the Executive Subcommittee of Committee D19, a statement giving a compelling reason why compliance with all or specific points of this practice cannot be achieved w
14、ill meet both ASTM requirements (1)2 and the related requirements of this practice. Precision-and- bias statements authorized by this paragraph shall include the date of approval by Committee D19.1.6 In principle, all test methods are covered by this practice.1.7 In Section 12 this practice shows ex
15、emplary precision- and-bias-statement formats for: (1) test methods yielding a numerical measure, (2) test methods yielding a non-numerical report of success or failure based on criteria specified in the procedure, and (3) test methods specifying that procedures in another ASTM test method are to be
16、 used with only insignifi- cant modifications.1.8 All studies, even those exempt from some requirements under 1.3 or 1.5, shall receive approval from the Results Advisor before being conducted (see Section 8) and after completion (see Section 13).1.9 This practice satisfies the QC requirements of Pr
17、actice D5847.1.10 It is the intent of this practice that task groups make every effort to retain all the data from their round-robin studies. Values should not be eliminated unless solid evidence exists for2 The boldface numbers in parentheses refer to the list of standards at the end of this practi
18、ce.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1D 2777 03 their exclusion. The Results Advisor should work closely withthe task groups to effect this goal.2. Referenced Documents2.1 ASTM Standards:D 1129 Terminology Relating to Wa
19、ter3D 1141 Specification for Substitute Ocean Water4D 1193 Specification for Reagent Water3D 4375 Practice for Basic Statistics in Committee D19 onWater3D 5790 Test Method for Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry4D 5847 Practice
20、 for Writing Quality Control Specifications for Standard Test Methods for Water Analysis4D 5905 Practice for the Preparation of Substitute Wastewa- ter3D 6091 Practice for 99 %/95 % Interlaboratory Detection Estimate (IDE) for Analytical Methods with Negligible Calibration Error3D 6512 Practice for
21、Interlaboratory Quantitation Estimate3E 177 Practice for Use of the Terms Precision and Bias inASTM Test Methods5E 178 Practice for Dealing with Outlying Observations5E 456 Terminology Relating to Quality and Statistics5E 1169 Guide for Conducting Ruggedness Tests53. Terminology3.1 DefinitionsFor de
22、finitions of terms used in this prac- tice, refer to Terminologies D 1129, D 4375 and E 456, and Practice E 177.3.2 Definitions of Terms Specific to This Standard:3.2.1 accuracya measure of the degree of conformity ofa single test result generated by a specific procedure to the assumed or accepted t
23、rue value, and includes both precision and bias.3.2.2 biasthe persistent positive or negative deviation of the average value of a test method from the assumed or accepted true value.3.2.3 laboratorya single and completely independent ana- lytical system with its own specific apparatus, source of rea
24、gents, set of internal standard-operating procedures, etc. Different laboratories will differ from each other in all of these aspects, regardless of how physically or organizationally close they may be to each other.3.2.4 operatorusually the individual analyst within each laboratory who performs the
25、 test method throughout the collaborative study. However, for complicated test methods, the operator may be a team of individuals, each performing a specific function throughout the study.3.2.5 precisionthe degree of agreement of repeated mea- surements of the same property, expressed in terms of di
26、sper- sion of test results about the arithmetical-mean result obtained by repetitive testing of a homogeneous sample under specified3 Annual Book of ASTM Standards, Vol 11.01.4 Annual Book of ASTM Standards, Vol 11.02.5 Annual Book of ASTM Standards, Vol 14.02.conditions. The precision of a test met
27、hod is expressedquantitatively as the standard deviation computed from the results of a series of controlled determinations.4. Summary of Practice4.1 After the task group has assured itself that the test method has had all preliminary evaluation work completed, the task group should prepare the test
28、-method write-up in final form. 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 except as specified in 1.3, 1.4, and 1.5. Upon receipt of concurrence, the collaborative test is
29、conducted, data analyzed, and precision-and-bias statements formulated by the task group. The final precision-and-bias statistics must be based on usable data from at least six independent laboratories. The statements, with backup data including the reported-results summary, the calculations leading
30、 up to the statements, and the test-method write-up with precision-and-bias statements included are sub- mitted to the subcommittee vice-chairman, who in turn sends a copy to the Results Advisor for concurrence before balloting. This procedure assures having an acceptable copy of the collaborative-s
31、tudy results to send to ASTM for items on the main-committee ballot. In most instances, the collaborative study shall be complete before a subcommittee ballot. If the collaborative study is not complete, the test method may go on the ballot as a provisional test method rather than a standard test me
32、thod. Copies of the test data, approved calculations, and statistical results shall be filed at ASTM Headquarters when the test method is submitted by the subcommittee chairman as an item for the main-committee ballot.4.1.1 The appendix shows an example of “Form AApproval of Plans for Interlaborator
33、y 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 calculation of precision and bias from real collaborative-test data, the related table of statistics, and the related precision-and-bias statement.5. Significance a
34、nd Use5.1 Following this practice should result in precision-and- bias statements that can be achieved by any laboratory properly using the test method studied. These precision-and-bias state- ments provide the basis for generic limits for use in the Quality Control section of the test method.5.2 Th
35、e method specifies the matrices for which the test method is appropriate. The collaborative test corroborates the write-up within the limitations of the test design. An extensive test can only use representative matrices so that universal applicability cannot be implied from the results.5.3 The fund
36、amental assumption of the collaborative study is that the matrices tested, the concentrations tested, and the participating laboratories are a representative and fair evalua- tion of the scope and applicability of the test method as written.2D 2777 03 6. Preliminary Studies6.1 Considerable pilot wor
37、k on a test method must precede the determination of its precision and bias (2,3). This pilot work should explore such variables as preservation require- ments, reaction time, concentration of reagents, interferences, calibration, and sample size. Potentially significant factors must be investigated
38、 and controlled in the written test method in advance of the collaborative test. Also, disregard of such factors may introduce so much variation among operators that results are misleading or inconclusive (4) (see 9.3 and 9.4). A ruggedness study conducted in a single laboratory is particu- larly us
39、eful for such investigations and should be conducted to prove a test method is ready for interlaboratory testing (see Guide E 1169 for details).6.2 Only after a proposed test method has been tried, proved, and reduced to unequivocal written form should a determination of its precision and bias be at
40、tempted.6.3 If the test method will require calculation of a detection estimate (for example, IDE, D 6091) or calculation of a quantitation estimate (for example, IQE, Practice Practice D6512), or both, then the following guidelines may be followed.6.3.1 To minimize the number of samples required, d
41、ata would be gathered in two phases:Phase ISingle-laboratory characterization. In this phase, the method developer would run a sufficient number of samples ata sufficient number of concentrations to characterize fully response vs. concentration, as well as error vs. concentration. The lowest concent
42、ration would be the level of the blank or the lowest concentration that could be measured; the highest concentration would be at the upper limit of the analytical range.Phase II. Collaborative study. Using the results of Phase I, the method developer would estimate the minimum number and the magnitu
43、de of concentrations necessary to meet the requirements of the documents of interest.7. Planning the Collaborative Test7.1 Based upon the task groups knowledge of a test method and the unequivocal write-up, several factors must be consid- ered in planning the collaborative test to assess the precisi
44、on of the test method properly. The testing variables that must be considered in planning are discussed below. In the collabora- tive study, it is generally not acceptable to control significant sources of variability that cannot be controlled in routine use of the test method, because this control
45、leads to false estimates of the test-method precision and bias. In addition, the task group must determine within the resources available how best to estimate the bias of the test method.7.2 Testing Variables:7.2.1 It is desirable to develop a test methods precision statement that indicates the cont
46、ribution to overall variation of selected causes such as laboratory, operator, sample matrix, analyte concentration, and other factors that may or have been shown to have strong effects on the results. Since any test method can be tried in only a limited number of applications, the standard deviation calculated from the results of a study can be only an estimate of the universe standard deviation. For this reason, the symbol s (sample standard deviation) is usedherein. The precision estimates generated from the study datawill usually be the overall
