ASTM E1488-2008a Standard Guide for Statistical Procedures to Use in Developing and Applying Test Methods.pdf

1、Designation: E 1488 08aAn American National StandardStandard Guide forStatistical Procedures to Use in Developing and ApplyingTest Methods1This standard is issued under the fixed designation E 1488; the number immediately following the designation indicates the year oforiginal adoption or, in the ca

2、se 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.1. Scope1.1 This guide identifies statistical procedures for use indeveloping new test methods or revi

3、sing or evaluating existingtest methods, or both.1.2 This guide also cites statistical procedures especiallyuseful in the application of test methods.2. Referenced Documents2.1 ASTM Standards:2E 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 178 Practice for Dealing With O

4、utlying ObservationsE 456 Terminology Relating to Quality and StatisticsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 1169 Practice for Conducting Ruggedness TestsE 2282 Guide for Defining the Test Result of a Test MethodE 2489 Practice for Statis

5、tical Analysis of One-Sample andTwo-Sample Interlaboratory Proficiency Testing ProgramsE 2554 Practice for Estimating and Monitoring the Uncer-tainty of Test Results of a Test Method in a SingleLaboratory Using a Control Sample ProgramE 2587 Practice for Use of Control Charts in StatisticalProcess C

6、ontrol2.2 ISO Standards:ISO 17025 General Requirements for the Competence ofTesting and Calibration Laboratories3ISO Guide to the Expression of Uncertainty in Measure-ment33. Terminology3.1 Definitions:3.1.1 statistical procedures, nthe organized techniquesand methods used to collect, analyze, and i

7、nterpret data.3.1.1.1 DiscussionStatistical procedures include the sam-pling considerations or the experiment design for the collectionof data, or both, and the numerical and graphical approaches tosummarize and analyze the collected data.3.2 For all other formal definitions of statistical terms, se

8、eTerminology E 456.4. Significance and Use4.1 All ASTM test methods are required to include state-ments on precision and bias.44.2 Since ASTM began to require all test methods to haveprecision and bias statements that are based on interlaboratorytest methods, there has been increased concern regardi

9、ng whatstatistical experiments and procedures to use during the devel-opment of the test methods. Although there exists a wide rangeof statistical procedures, there is a small group of generallyaccepted techniques that are very beneficial to follow. Thisdocument is designed to provide a brief overvi

10、ew of theseprocedures and to suggest an appropriate sequence of carryingout these procedures.4.3 Statistical procedures often result in interpretations thatare not absolutes. Sometimes the information obtained may beinadequate or incomplete, which may lead to additional ques-tions and the need for f

11、urther experimentation. Informationoutside the data is also important in establishing standards andin the interpretation of numerical results.5. Summary of Guide5.1 Outlined below is a suggested sequence of four phasesuseful in the development of a test method. A flowchart isprovided in Fig. 1. Such

12、 a sequence of analyses may need to bemodified in specific situations. The assistance of a qualifiedstatistician is recommended at each review phase.5.2 Design Phase:5.2.1 This phase includes the formalization of the scope andthe significance and use sections. It may include determining1This guide i

13、s under the jurisdiction of ASTM Committee E11 on Quality andStatistics and is the direct responsibility of Subcommittee E11.20 on Test MethodEvaluation and Quality Control.Current edition approved Oct. 1, 2008. Published October 2008. Originallyapproved in 1992. Last previous edition approved in 20

14、08 as E 1488 08.2For referenced ASTM standards, 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.3Available from American National Standards I

15、nstitute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4See the Form and Style Manual for ASTM Standards that specifies, whenpossible, precision statements shall be estimated based on the results of aninterlaboratory test program.1Copyright ASTM International, 100 Barr Har

16、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the purpose and describing a general approach to the testmethod but usually does not involve statistical studies.5.3 Development Phase5.3.1 Studies may be conducted to evaluate the basicperformance of the method. The draft test

17、method is preparedand sampling requirements and the test result (see GuideE 2282) are clearly defined.5.3.2 A flow chart is extremely valuable to identify thesequence of operations involved in a test method, for example,the sampling steps required to obtain the test specimens,definition of the test

18、determination, how a test result is to becomputed, and running the tests on the specimens.5.4 Validation Phase5.4.1 The test method is examined for such concerns as itsstability, ruggedness, statistical control and the contributions tovariability. The completion of this phase should result inprelimi

19、nary estimates of precision and the identification andsuggested ways to estimate potential contributors to uncer-tainty.5.4.2 Evaluation of Short Term Control of Test Method Atest method must exhibit an ability to provide consistent resultsat least over short time periods. Preliminary studies or a p

20、ilottest should be conducted to evaluate the short term stability ofthe test method. A small series of repeated tests should beconducted.5.4.3 Analysis of VariabilityStatistically designed experi-ments conducted in one or two laboratories can be used toassess the relative magnitudes of different sou

21、rces or potentialcontributors to variability of the test results. Such studies canprovide estimates of intermediate measures of precision.5.4.4 Ruggedness TestA ruggedness test (see PracticeE 1169) is a statistically designed experiment that helps iden-tify problems in running the test method, clari

22、fies errors, andpoints out possible environmental conditions, which mayadversely affect the test method or point out need for tighteningrequirements. The ruggedness test can assist in locating waysof reducing variability in the test method.5.4.5 Preliminary Estimates of Precision From the vari-ous s

23、tudies conducted in accordance with 5.4.25.4.4, prelimi-nary estimates of repeatability standard deviations should bedeveloped and published in this test method. Until an inter-laboratory study is performed, these estimates generally areconsidered to be provisional. Information on how a lab shouldde

24、velop uncertainty estimates should also be provided.5.4.6 Statistical ControlA test method must show capa-bility of performing in a consistent way over time. The use ofcontrol charts (see Manual 7)4to monitor a proposed, orexisting, test method over time is one recommended way toexamine the controll

25、ability or stability of a test method. ThisFIG. 1 Sequence of StepsE 1488 08a2statistical control should be demonstrated in one or twolaboratories using homogeneous material (test specimen).5.5 Evaluation Phase:5.5.1 The test method is subjected to interlaboratory studiesto provide estimates of with

26、in-laboratory repeatability andbetween-laboratory reproducibility. Additional information issupplied from proficiency studies when conducted.5.5.2 Interlaboratory Study (ILS)In accordance withASTM Form and Style Manual, whenever feasible, an inter-laboratory study must be conducted. This procedure w

27、illprovide specific estimates of variation anticipated when usingthe test method.5.5.3 Protocol for the ILS, Practice E 691 provides a guidefor developing the ILS for the test method. A first step is thewriting of an ILS Protocol, which will set out what needs to bedone before the test specimens (or

28、 test materials) are distrib-uted to the participating laboratories.5.5.4 Precision StatementsUsing the estimates of varia-tion obtained in the interlaboratory test, one may prepareprecision statements using Practices E 691 and E 177 orequivalent procedures.6. Development of Test Method Sampling and

29、 TestResult6.1 Proposed standards that are under development shouldbe treated in a formal manner following as many of thesuggested procedures as possible. Standards that are already inexistence as approved test methods or in general practicerequire periodic review that would include selected procedu

30、res.6.2 Under DevelopmentThe development stage involvestest methods that are in the preliminary stages during whichequipment may not have been fully tested, practices are notagreed upon, and operators have yet to be adequately trained.Often this stage also applies to standards that have not yet been

31、approved.6.2.1 It is essential that tests for statistical control, rugged-ness, and variability analyses be conducted prior to anyinterlaboratory test programs.6.2.2 After all major environmental contributors have beenidentified, controlled, and incorporated into the test method,and after adequate s

32、tandardized equipment is available, aninterlaboratory test can be conducted. The interlaboratory testprogram must be completed prior to the first 5-year review. Thecommittee should strive to have interlaboratory results as soonas possible.6.2.3 After evaluating data from ruggedness tests, variabil-i

33、ty analysis, or an interlaboratory test program, changes to thetest method may be suggested.6.2.4 If major changes are made to the test method, a repeatof the various steps is usually necessary. Precision and biasstatements should reflect the most current version of the testmethod.6.3 Existing Stand

34、ardsThese standards comprise testmethods that are in common use for which standard equipmentmay exist and for which experienced operators have beentrained and are available.6.3.1 Control charting, ruggedness tests, and variabilityanalyses will be useful, especially if they have not previouslybeen co

35、nducted. Such tests may provide better informationabout variation and necessary tolerances than has previouslybeen available.6.3.2 If precision estimates have not been establishedthrough an actual interlaboratory test program, then such aprogram should be initiated.7. Data and Sampling7.1 Sample Det

36、ermination:7.1.1 The sampling section of a standard should indicateclearly what constitutes the primary sampling unit, how thatsampling unit is further subdivided, and how multiple testvalues are designated.7.1.2 In considering the implication of test results as theyrelate to the material, the test

37、method should be clear as towhether the sampling method or the test is destructive ornondestructive.7.1.3 The user of the test method should be aware ofwhether the standard calls for a random sample. In somestandards, as for example in sampling from coils or rolls ofmaterial, samples may be taken on

38、ly from certain portions ofthe material.7.2 Test Result DeterminationThe procedure for deter-mining a test result must be clear and unambiguous.7.2.1 An observation leads to an observed value.7.2.2 Several observed values may lead to a test determina-tion. The observed values need not be the same ty

39、pe ofmeasurements (for example, they may consist of three readingssuch as length, width, and mass).7.2.3 Several Test determinations may lead to a test result,as by averaging three test determinations.7.2.4 A test result is the consequence of a single executionof the entire test method.7.3 Type of D

40、ataThe kind of data that results from theapplication of the test method determines the types of statisticalanalyses to be performed.7.3.1 Numerical versus Categorical/Attribute DataMostof the statistical procedures referred to in this standard dealwith numerical data. Control charts are available fo

41、r all typesof data, but all interlaboratory test procedures currently in usedepend on numerical data.7.3.2 “Normally” Distributed DataMost of the statisticalprocedures referred to in this guide consider that the unknowndistribution of the test results can be modeled by a normaldistribution.8. Source

42、s of Variability8.1 Experimental Realization of a Test Method8.1.1 A realization of a test method refers to an actualapplication of the test method to produce a test result asspecified by the test method. The realization involves aninterpretation of the written document by a specific testoperator ,

43、who uses a specific unit and version of the specifiedtest apparatus, in the particular environment of his testinglaboratory, to evaluate a specified number of test specimens ofthe material to be tested. Another realization of the test methodmay involve a change in one or more of the above emphasized

44、experimental factors. The test result obtained by anotherrealization of the test method will usually differ from the testE 1488 08a3result obtained from the first realization. Even when none ofthe experimental factors is intentionally changed, smallchanges usually occur. The outcome of these changes

45、 may beseen as variability among the test results.8.1.2 Each of the above experimental factors and all others,known and unknown, that can change the realization of a testmethod, are potential sources of variability in test results. Someof the more common factors are discussed in Sections 8.2 to8.68.

46、2 Operator8.2.1 Clarity of Test Method Every effort must be made inpreparing an ASTM standard test method to eliminate thepossibility of serious differences in interpretation. One way tocheck clarity is to observe, without comment, a competentlaboratory technician, not previously familiar with the m

47、ethod,apply the draft test method. If the technician has any difficulty,the draft most likely needs revision.8.2.2 Completeness of Test Method It is necessary thattechnicians, who are generally familiar with the test method orsimilar methods, not read anything into the instructions that isnot explic

48、itly stated therein. Therefore, to ensure minimumvariability due to interpretation, procedural requirements mustbe complete.8.2.3 Differences in Operator Technique Even whenoperators have been trained by the same teacher or supervisorto give practically identical interpretations to the various steps

49、of the test method, different operators (or even the sameoperator at different times) may still differ in such things asdexterity, reaction time, color sensitivity, interpolation in scalereading, and so forth. Unavoidable operator differences arethus one source of variability between test results. The testmethod should be designed and described to minimize theeffects of these operator sources of variability.8.3 Apparatus8.3.1 Tolerances In order to avoid prohibitive costs, onlynecessary and reasonable manufacturing and maintenancetolerances can be specifi