1、Designation: C670 13C670 15Standard Practice forPreparing Precision and Bias Statements for Test Methodsfor Construction Materials1This standard is issued under the fixed designation C670; 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 The Form and
3、Style for ASTM Standards requires that all test methods contain statements on precision and bias. Further,the precision statement is required to contain a statement on single-operator precision (repeatability) and a statement onmultilaboratory precision (reproducibility). This practice provides guid
4、ance for preparing precision and bias statements thatcomply with these requirements. Discussion of the purpose and significance of precision and bias statements for users of testmethods is also provided. Examples of precision statements that conform to this practice are included in Appendix X1. This
5、practice supplements Practice E177 and has been developed to meet the needs of ASTM Committees dealing with constructionmaterials.NOTE 1Although this practice is under the jurisdiction of Committee C09, the current version was developed jointly by Committees C01 and C09and has subsequently been adop
6、ted for use by other committees dealing with construction materials.1.2 This practice assumes that an interlaboratory study (ILS) has been completed in accordance with Practice C802 or PracticeE691. The interlaboratory study provides the necessary statistical values to write the precision and bias s
7、tatements.1.3 The system of units for this practice is not specified. Dimensional quantities in the practice are presented only in examplesof precision and bias statements.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibil
8、ityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C802 Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Method
9、s for ConstructionMaterialsC1067 Practice for Conducting a Ruggedness Evaluation or Screening Program for Test Methods for Construction MaterialsD6607 Practice for Inclusion of Precision Statement Variation in Specification LimitsE177 Practice for Use of the Terms Precision and Bias in ASTM Test Met
10、hodsE456 Terminology Relating to Quality and StatisticsE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1 For definitions of general statistical terms, refer to Terminology E456.3.2 Definitions of Terms Specific to Thi
11、s Standard:33.2.1 test determination, nthe value of a characteristic of a single test specimen obtained by a specified test method.1 This practice is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee C09.94 onEvaluation
12、of Data (Joint C09 and C01).Current edition approved July 1, 2013June 15, 2015. Published July 2013August 2015. Originally approved in 1971. Last previous edition approved in 20102013 asC670C670 13.-10. DOI: 10.1520/C0670-13.10.1520/C0670-15.2 For referencedASTM standards, visit theASTM website, www
13、.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Terms are listed in order of hierarchy beginning with the basic concept.This document is not an ASTM standard and is
14、intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the c
15、urrent versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.1.1 DiscussionThe term “
16、replicate“ is often used for a test determination.3.2.2 test result, nthe value of a characteristic of a material obtained by carrying out a specified test method.3.2.2.1 DiscussionA test result may be a single test determination or the average of a specified number of test determinations, or replic
17、ates (see 4.1for additional discussion).3.2.3 identical test specimens, ntest specimens selected at random and made from a single quantity or batch of material thatis as homogeneous as possible.3.2.3.1 DiscussionIn interlaboratory studies of test methods for fresh cementitious mixtures, a practicabl
18、e approach for obtaining identical testsspecimens is to assemble technicians from different laboratories at one location and test specimens are made from the same batchof the fresh mixture. For interlaboratory studies of nondestructive test methods, the same test specimens can be circulated amongpar
19、ticipating laboratories, provided the characteristic of interest does not change during the time to complete the study.3.2.4 single-operator standard deviation, sr, (or coeffcient of variation, CVr), nthe standard deviation (or coefficient ofvariation) of test determinations obtained on identical te
20、st specimens by a single operator using the same apparatus in the samelaboratory over a relatively short period of time.3.2.4.1 DiscussionThe single-operator standard deviation, or coefficient of variation, is the fundamental statistic underlying the single-operatorindexes of precision. The single-o
21、perator standard deviation, or coefficient of variation, is an indication of the variability of a largegroup of test determinations by the same operator on the same material. This value is obtained from an interlaboratory study andis equal to the pooled standard deviation of test determinations obta
22、ined by the operators. The coefficient of variation (ratio ofstandard deviation to the average expressed as a percentage) is used if the standard deviation is proportional to the level of thecharacteristic being measured. The single-operator standard deviation, usually considered a property of the t
23、est method, willgenerally be lower than the multilaboratory standard deviation. In Practice E177, the single-operator standard deviation is referredto as the repeatability standard deviation, and the subscript r is used. In previous versions of Practice C670, the terms one-sigmalimit (1s) or one sig
24、ma limit in percent (1s%) were used for the single-operator standard deviation or single-operator coefficientof variation, respectively. In some publications, the term within-test standard deviation (or coeffcient of variation) has been used.The term within-laboratory standard deviation (or coeffici
25、ent of variation) should not be used for this statistic (see 4.2.3).3.2.5 multilaboratory standard deviation, sR (or coeffcient of variation, CVR), nthe standard deviation or coefficient ofvariation of test results obtained with the same test method on identical test specimens in different laborator
26、ies with differentoperators using different equipment.3.2.5.1 DiscussionThe multilaboratory standard deviation, or coefficient of variation, is the fundamental statistic underlying the indexes of precisionunder multilaboratory conditions. The multilaboratory standard deviation is an indication of th
27、e variability of a group of test resultsobtained by different laboratories for identical test specimens. The multilaboratory standard deviation (or coefficient of variation)is usually greater than the single-operator standard deviation (or coefficient of variation), because different operators and d
28、ifferentapparatus have been used in different laboratories for which the environments may have differed. In Practice E177, themultilaboratory standard deviation is referred to as the reproducibility standard deviation and the subscript R is used.3.2.6 difference limit (d2s or d2s%), nthe difference
29、between two test results that is expected to be exceeded with a probabilityof about 5 % in the normal and correct operation of the test method; used as an index of precision of the test method.3.2.6.1 DiscussionThe difference limit has been selected as the appropriate index of precision in most prec
30、ision statements. A difference limit (d2s)indicates the maximum acceptable difference between two results obtained on identical test specimens (see 3.2.3.1) under theapplicable system of causes (single-operator or multilaboratory conditions). The (d2s%) limit is the maximum acceptabledifference betw
31、een two test results expressed as a percentage of their average. These difference limits are calculated by multiplyingC670 152the appropriate standard deviation (sr or sR) or coefficient of variation (CVr or CVR) by the factor 1.96 =2, which for the purposeof this Practice is taken to be equal to 2.
32、8. In Practice E177, the terms repeatability limit and reproducibility limit are used for thesedifference limits under single-operator and multilaboratory conditions, respectively.3.2.7 acceptable range, nthe difference between the largest and smallest of three or more test determinations or test re
33、sultsthat is expected to be exceeded with a probability of about 5 % in the normal and correct operation of the test method; used asan index of precision of the test method, if applicable.3.2.7.1 DiscussionThis index is usually reported in precision statements of test methods that define a test resu
34、lt as the average of three or moredeterminations. Otherwise, the difference limit (d2s or d2s%) is used. See 4.3 for additional discussion on how to determine thisindex.4. General Concepts4.1 Test ResultThe result of a test method may be a single test determination or the average of two or more test
35、 determinations(or replicates). The precision statement of a test method applies to a test result as defined in the test method and should state clearlythis fact.4.1.1 Number of Test DeterminationsThe number of test determinations required to obtain a test result by a test method mustbe taken into a
36、ccount when evaluating testing variations. The statistic used in evaluating single-operator precision is based usuallyon the standard deviation (or coefficient of variation) of single test determinations. The single-operator standard deviation (orcoefficient of variation) may be used in evaluating t
37、he acceptable range of test determinations.4.1.2 Test Result Based on Averages of DeterminationsFor test methods that define a test result as the average of two or moretest determinations (or replicates), the fundamental statistic is still the standard deviation (or coefficient of variation) of sing
38、le testdeterminations. The report of the analysis of the interlaboratory study (see 5.2) must include this statistic. The single-operatorstandard deviation of test determinations can be used to calculate the standard deviation of a test result that is the average ofmultiple determinations and thereb
39、y define the maximum acceptable difference between two test results obtained by the sameoperator on identical test specimens. The precision statement may also include the maximum acceptable range of individualdeterminations that comprise the test result (see 4.3).4.1.3 Standard Deviation of an Avera
40、geThe standard deviation of the average of n test determinations obtained from identicalspecimens taken from the same population is equal to the standard deviation of the individual determinations divided by the squareroot of n. This relationship is valid, however, only if the determinations are obt
41、ained using identical specimens. It is not applicableto averages obtained on specimens made from different batches of cementitious mixtures as discussed in 4.2.3.4.2 Types of PrecisionA precision statement meeting the requirements of this practice normally contains two main elements:(1) single-opera
42、tor precision, and (2) multilaboratory precision. For test methods that require test results on specimens made frommore than one batch, the single-operator, multi-batch precision is also included.4.2.1 Single-Operator PrecisionThe pooled, single-operator standard deviation (or coefficient of variati
43、on) of test determi-nations obtained from the interlaboratory study is the underlying statistic of the test method. This is used to calculate the greatestdifference between two or more determinations that would be considered acceptable when properly conducted repetitivedeterminations are made on the
44、 same material by a competent operator. As discussed in 4.1.2, the single-operator standarddeviation (or coefficient of variation) of test determinations is also used to calculate the greatest acceptable difference between testresults defined as the average of two or more determinations. The single-
45、operator precision provides a quantitative guide toacceptable performance by an operator. If two determinations or test results by the same operator differ by more than the differencelimit, (d2s) or (d2s%), or if the range of more than two determinations or test results exceeds the values defined in
46、 4.3, there isa high probability that an error has occurred and retests should be made.NOTE 2It is beyond the scope of this practice to describe in detail what action should be taken in all cases if two test results differ by more than the(d2s) or (d2s%) limits or the range of more than two determin
47、ations exceeds the maximum expected range. Such an occurrence is a warning that theremay have been some error in the test procedure, or some departure from the prescribed conditions of the test on which the limits appearing in the testmethod are based; for example, faulty or misadjusted apparatus or
48、 improper conditions in the laboratory. In judging whether or not results are in error,information other than the difference between two test results is needed. Often a review of the circumstances under which the test results in question wereobtained will reveal some reason for a departure. In this
49、case, the data should be discarded and new test results obtained and evaluated separately. If nophysical reason for a departure is found, retests should still be made, but the original tests should not be ignored. If the second set of results also differsby more than the applicable limit, the evidence is very strong that something is wrong or that a real difference exists between the specimens tested. Ifthe second set produces a result within the limit, it may be taken as a valid test, but the operator or laboratory may then be suspected of producing errat
