1、Designation: E691 13 An 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,
2、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.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTION
3、Tests 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 controlle
4、d. 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 specifi
5、ed 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 laboratories
7、changes 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 of
8、time 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 accepte
9、dreference 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, whenev
10、aluating 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 thefact
11、ors 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 con
12、tributing 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
13、a 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 se
14、nt 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 unusua
15、l steps to get “good” results. It is alsoimportant to recognize and consider how to treat “poor” results that may have unacceptable assignablecauses (for example, departures from the prescribed procedure). The inclusion of such results in theCopyright ASTM International, 100 Barr Harbor Drive, PO Bo
16、x C700, West Conshohocken, PA 19428-2959. United States1final 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,operations, 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 establish1This practice is under the jurisdiction of ASTM Committee E11 on Qual
29、ity and Statistics and is the direct responsibility of Subcommittee E11.20 on Test MethodEvaluation and Quality Control.Current edition approved May 1, 2013. Published May 2013. Originally approved in 1979. Last previous edition approved in 2012 as E691 12. DOI: 10.1520/E0691-13.E691 132appropriate
30、safety and health practices and determine theapplicability 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 StatisticsE1169 Practice for Conducting Rugge
31、dness TestsE1402 Guide for Sampling DesignE2282 Guide for Defining the Test Result of a Test Method3. Terminology3.1 DefinitionsTerminology E456 provides a more exten-sive list of terms in E11 standards.3.1.1 accuracy, nthe closeness of agreement between atest result and an accepted reference value.
32、 E1773.1.2 bias, nthe difference between the expectation of thetest results and an accepted reference 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 testresul
33、ts on one or more materials.3.1.4 observation, nthe process of obtaining informationregarding the 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 te
34、st results obtained under stipulated conditions.E1773.1.6 repeatability, nprecision under repeatabilityconditions. 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
35、 the same equipment within short intervals of time. E1773.1.8 repeatability limit (r), nthe value below which theabsolute difference between two individual test results obtainedunder repeatability conditions may be expected to occur with aprobability of approximately 0.95 (95 %). E1773.1.9 repeatabi
36、lity standard deviation, (sr), nthe standarddeviation of test result obtained under repeatability conditions.E1773.1.10 reproducibility, nprecision under reproducibilityconditions. E1773.1.11 reproducibility conditions, nconditions where testresults are obtained with the same method on identical tes
37、titems in different laboratories with different operators usingdifferent equipment. E1773.1.12 reproducibility limit (R), nthe value below whichthe absolute difference between two test results obtained underreproducibility conditions may be expected to occur with aprobability of approximately 0.95 (
38、95 %). E1773.1.13 reproducibility standard deviation (sR), nthe stan-dard deviation of test results obtained under reproducibilityconditions. E1773.1.14 ruggedness test, na planned experiment in whichenvironmental factors or test conditions are deliberately variedin order to evaluate the effects of
39、such variation. E11693.1.15 test determination, nthe value of a characteristic ordimension of a single test specimen derived from one or moreobserved values. E22823.1.16 test method, na definitive procedure that producesa test result. E22823.1.17 test observation, nsee observation. E22823.1.18 test
40、result, nthe value of a characteristic obtainedby carrying out a specified test method. E22823.1.19 test specimen, nthe portion of a test sample neededto obtain a single test determination. E22823.1.20 test sample, nthe total quantity of material (con-taining one or more test specimens) needed to ob
41、tain a testresult as specified in the test method; see test result. E22823.2 Definitions of Terms Specific to This Standard:3.2.1 average of the cell averages, x=,nthe average of thecell averages for a particular material.3.2.2 between-laboratory consistency statistic, h, ntheratio of the cell devia
42、tion to the standard deviation of the cellaverages.3.2.2.1 DiscussionThis statistic is an indicator of how onelaboratorys cell average compares with the average of theother laboratories for a particular material (see X1.2.2).3.2.3 cell, nthe intersection of a row and column in atwo-way classificatio
43、n table, in which the rows represent thelaboratories and the columns represent the materials.3.2.3.1 DiscussionThe table holds the test results from aninterlaboratory study, and each cell contains the test resultsfrom a particular laboratory on a particular material (seeSection 7 and Table 1).3.2.4
44、cell average, x, nthe average of the test results in aparticular cell.3.2.5 cell deviation, d, nthe cell average minus the aver-age of the cell averages.3.2.6 cell standard deviation, s, nthe standard deviation ofthe test results in a particular cell.3.2.7 standard deviation of the cell averages, sx
45、,nthestandard deviation of the cell averages for a particular material.3.2.8 within-laboratory consistency statistic, k, nthe ratioof the cell standard deviation to the repeatability standarddeviation.3.2.8.1 DiscussionThis statistic is an indicator of how onelaboratorys cell standard deviation unde
46、r repeatability condi-tions compares with the repeatability standard deviation esti-mated from all laboratories for a particular material (seeX1.2.3).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStand
47、ards volume information, refer to the standards Document Summary page onthe ASTM website.E691 1334. Summary of Practice4.1 The procedure presented in this practice consists ofthree basic steps: planning the interlaboratory study, guidingthe testing phase of the study, and analyzing the test result d
48、ata.The analysis utilizes tabular, graphical, and statistical diagnos-tic tools for evaluating the consistency of the data so thatunusual values may be detected and investigated, and alsoincludes the calculation of the numerical measures of precisionof the test method pertaining to both within-labor
49、atory repeat-ability and between-laboratory reproducibility.5. Significance and Use5.1 ASTM regulations require precision statements in alltest methods in terms 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 for the actual measurement processand for the written description of the process, w
