1、Designation: E691 11An American National StandardStandard Practice forConducting an Interlaboratory Study to Determine thePrecision of a Test Method1This standard is issued under the fixed designation E691; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n 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.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTIONT
3、ests performed on presumably identical materials in presumably identical circumstances do not, ingeneral, yield identical results. This is attributed to unavoidable random errors inherent in every testprocedure; the factors that may influence the outcome of a test cannot all be completely controlled
4、. Inthe practical interpretation of test data, this inherent variability has to be taken into account. Forinstance, the difference between a test result and some specified value may be within that which canbe expected due to unavoidable random errors, in which case a real deviation from the specifie
5、d valuehas not been demonstrated. Similarly, the difference between test results from two batches of materialwill not indicate a fundamental quality difference if the difference is no more than can be attributedto inherent variability in the test procedure. Many different factors (apart from random
6、variationsbetween supposedly identical specimens) may contribute to the variability in application of a testmethod, including: a the operator, b equipment used, c calibration of the equipment, and denvironment (temperature, humidity, air pollution, etc.). It is considered that changing laboratoriesc
7、hanges each of the above factors. The variability between test results obtained by different operatorsor with different equipment will usually be greater than between test results obtained by a singleoperator using the same equipment. The variability between test results taken over a long period oft
8、ime even by the same operator will usually be greater than that obtained over a short period of timebecause of the greater possibility of changes in each of the above factors, especially the environment.The general term for expressing the closeness of test results to the “true” value or the accepted
9、reference value is accuracy. To be of practical value, standard procedures are required for determiningthe accuracy of a test method, both in terms of its bias and in terms of its precision. This practiceprovides a standard procedure for determining the precision of a test method. Precision, wheneva
10、luating test methods, is expressed in terms of two measurement concepts, repeatability andreproducibility. Under repeatability conditions the factors listed above are kept or remain reasonablyconstant and usually contribute only minimally to the variability. Under reproducibility conditions thefacto
11、rs are generally different (that is, they change from laboratory to laboratory) and usuallycontribute appreciably to the variability of test results. Thus, repeatability and reproducibility are twopractical extremes of precision.The repeatability measure, by excluding the factors a through d as cont
12、ributing variables, is notintended as a mechanism for verifying the ability of a laboratory to maintain“ in-control” conditionsfor routine operational factors such as operator-to-operator and equipment differences or any effectsof longer time intervals between test results. Such a control study is a
13、 separate issue for eachlaboratory to consider for itself, and is not a recommended part of an interlaboratory study.The reproducibility measure (including the factors a through d as sources of variability) reflectswhat precision might be expected when random portions of a homogeneous sample are sen
14、t to random“in-control” laboratories.To obtain reasonable estimates of repeatability and reproducibility precision, it is necessary in aninterlaboratory study to guard against excessively sanitized data in the sense that only the uniquelybest operators are involved or that a laboratory takes unusual
15、 steps to get “good” results. It is alsoimportant to recognize and consider how to treat “poor” results that may have unacceptable assignable1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.causes (for example, departures from the pre
16、scribed procedure). The inclusion of such results in thefinal precision estimates might be questioned.An essential aspect of collecting useful consistent data is careful planning and conduct of the study.Questions concerning the number of laboratories required for a successful study as well as the n
17、umberof test results per laboratory affect the confidence in the precision statements resulting from the study.Other issues involve the number, range, and types of materials to be selected for the study, and theneed for a well-written test method and careful instructions to the participating laborat
18、ories.To evaluate the consistency of the data obtained in an interlaboratory study, two statistics may beused: the “k-value”, used to examine the consistency of the within-laboratory precision fromlaboratory to laboratory, and the “h-value”, used to examine the consistency of the test results fromla
19、boratory to laboratory. Graphical as well as tabular diagnostic tools help in these examinations.1. Scope1.1 This practice describes the techniques for planning,conducting, analyzing, and treating the results of an interlabo-ratory study (ILS) of a test method. The statistical techniquesdescribed in
20、 this practice provide adequate information forformulating the precision statement of a test method.1.2 This practice does not concern itself with the develop-ment of test methods but rather with gathering the informationneeded for a test method precision statement after the devel-opment stage has b
21、een successfully completed. The dataobtained in the interlaboratory study may indicate, however,that further effort is needed to improve the test method.1.3 Since the primary purpose of this practice is the devel-opment of the information needed for a precision statement, theexperimental design in t
22、his practice may not be optimum forevaluating materials, apparatus, or individual laboratories.1.4 Field of ApplicationThis practice is concerned exclu-sively with test methods which yield a single numerical figureas the test result, although the single figure may be the outcomeof a calculation from
23、 a set of measurements.1.4.1 This practice does not cover methods in which themeasurement is a categorization, such as a go-no-go allocation(two categories) or a sorting scheme into two or morecategories. For practical purposes, the discontinuous nature ofmeasurements of these types may be ignored w
24、hen a test resultis defined as an average of several individual measurements.Then, this practice may be applicable, but caution is requiredand a statistician should be consulted.1.5 The information in this practice is arranged as follows:SectionScope 1Referenced Documents 2Terminology 3Summary of Pr
25、actice 4Significance and Use 5Planning the Interlaboratory Study (ILS) SectionILS Membership 6Basic Design 7Test Method 8Laboratories 9Materials 10Number of Test Results per Material 11Protocol 12Conducting the Testing Phase of the ILS SectionPilot Run 13Full Scale Run 14Calculation and Display of S
26、tatistics SectionCalculation of the Statistics 15Tabular and Graphical Display of Statistics 16Data Consistency SectionFlagging Inconsistent Results 17Investigation 18Task Group Actions 19Examples of Interlaboratory Studies 20Precision Statement Information SectionRepeatability and Reproducibility 2
27、1Appendixes AppendixTheoretical Considerations X1Index to Selected Terms X2ReferencesTables and FiguresTableGlucose in Serum Example 14, 67, 11Pentosans in Pulp Example 810, 12Critical Values of Consistency Statistics, h and k 5FigureGlucose in Serum Example 14, 8Pentosans in Pulp Example 57, 91.6 T
28、his standard may involve hazardous materials, opera-tions, and equipment. This standard does not purport toaddress all of the safety problems associated with its use. It isthe responsibility of the user of this standard to establishappropriate safety and health practices and determine theapplicabili
29、ty of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE456 Terminology Relating to Quality and Statistics1This practice is under the jurisdiction of ASTM Committee E11 on Quality and Statistics an
30、d is the direct responsibility of Subcommittee E11.20 on Test MethodEvaluation and Quality Control.Current edition approved Nov. 1, 2011. Published November 2011. Originally approved in 1979. Last previous edition approved in 2009 as E691 091. DOI:10.1520/E0691-11.2For referenced ASTM standards, vis
31、it 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.E691 112E1169 Practice for Conducting Ruggedness TestsE2282 Guide for Defining the Test Result o
32、f a Test Method3. Terminology3.1 Terminology E456 provides a more extensive list ofterms in E11 standards.3.1.1 accuracy, nthe closeness of agreement between atest result and an accepted reference value. E1773.1.2 bias, nthe difference between the expectation of thetest results and an accepted refer
33、ence value. E1773.1.3 interlaboratory study, (ILS) in ASTM, na designedprocedure for obtaining a precision statement for a test method,involving multiple laboratories, each generating replicate testresults on one or more materials.3.1.4 observation, nthe process of obtaining informationregarding the
34、 presence or absence of an attribute of a testspecimen, or of making a reading on a characteristic ordimension of a test specimen. E22823.1.5 precision, nthe closeness of agreements betweenindependent test results obtained under stipulated conditions.E1773.1.6 repeatability, nprecision under repeata
35、bility condi-tions. E1773.1.7 repeatability conditions, nconditions where inde-pendent test results are obtained with the same method onidentical test items in the same laboratory by the same operatorusing the same equipment within short intervals of time.E1773.1.8 repeatability standard deviation,
36、(Sr), nthe standarddeviation of test result obtained under repeatability conditions.E1773.1.9 reproducibility, nprecision under reproducibilityconditions. E1773.1.10 reproducibility conditions, nconditions where testresults are obtained with the same method on identical testitems in different labora
37、tories with different operators usingdifferent equipment. E1773.1.11 reproducibility standard deviation (SR), nthe stan-dard deviation of test results obtained under reproducibilityconditions. E1773.1.12 test determination, nthe value of a characteristic ordimension of a single test specimen derived
38、 from one or moreobserved values. E22823.1.13 test method, na definitive procedure that producesa test result. E22823.1.14 test observation, nsee observation.3.1.15 test result, nthe value of a characteristic obtainedby carrying out a specified test method. E22823.1.16 test specimen, nthe portion of
39、 a test unit needed toobtain a single test determination. E22823.1.17 test unit, nthe total quantity of material (containingone or more test specimens) needed to obtain a test result asspecified in the test method; see test result. E22824. Summary of Practice4.1 The procedure presented in this pract
40、ice consists ofthree basic steps: planning the interlaboratory study, guidingthe testing phase of the study, and analyzing the test result data.The analysis utilizes tabular, graphical, and statistical diagnos-tic tools for evaluating the consistency of the data so thatunusual values may be detected
41、 and investigated, and alsoincludes the calculation of the numerical measures of precisionof the test method pertaining to both within-laboratory repeat-ability and between-laboratory reproducibility.5. Significance and Use5.1 ASTM regulations require precision statements in alltest methods in terms
42、 of repeatability and reproducibility. Thispractice may be used in obtaining the needed information assimply as possible. This information may then be used toprepare a precision statement in accordance with PracticeE177.5.2 Test Method and ProtocolIn this practice, the term“test method” is used both
43、 for the actual measurement processand for the written description of the process, while the term“protocol” is used for the directions given to the laboratoriesfor conducting the ILS.5.3 Observations, Test Determinations and Test Results:5.3.1 Atest method often has three distinct stages, the direct
44、observation of dimensions or properties, the arithmetic combi-nation of the observed values to obtain a test determination,and the arithmetic combination of a number of test determina-tions to obtain the test result of the test method. In the simplestof test methods a single direct observation is bo
45、th the testdetermination and the test result. For example, the test methodmay require the measurement of the mass of a test specimenprepared in a prescribed way.Another test method may requirethe measurement of the area of the test specimen as well as themass, and then direct that the mass be divide
46、d by the area toobtain the mass per unit area of the specimen. The wholeprocess of measuring the mass and the area and calculating themass per unit area is a test determination. If the test methodspecifies that only one test determination is to be made, thenthe test determination value is the test r
47、esult of the test method.Some test methods require that several determinations be madeand the values obtained be averaged or otherwise combined toobtain the test result of the test method. Averaging of severaldeterminations is often used to reduce the effect of localvariations of the property within
48、 the material.5.3.2 In this practice, the term “test determination” is usedboth for the process and for the value obtained by the process,except when “test determination value” is needed for clarity.5.3.3 The number of test determinations required for a testresult should be specified in each individ
49、ual test method. Thenumber of test results required for an interlaboratory study ofa test method is specified in the protocol of that study.5.4 Test Specimens and Test UnitsIn this practice a testunit is the total quantity of material needed for obtaining a testresult as specified by the test method. The portion of the testunit needed for obtaining a single test determination is called atest specimen. Usually a separate test specimen is required foreach test determination.5.5 Precision, Bias, and Accuracy of a Test Method:5.5.1 When a test method is applied
