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ASTM E691-15

(Practice)

Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

SIGNIFICANCE AND USE
4.1 ASTM regulations require precision statements in all test methods in terms of repeatability and reproducibility. This practice may be used in obtaining the needed information as simply as possible. This information may then be used to prepare a precision statement in accordance with Practice E177. Knowledge of the test method precision is useful in commerce and in technical work when comparing test results against standard values (such as specification limits) or between data sources (different laboratories, instruments, etc.).  
4.1.1 When a test method is applied to a large number of portions of a material that are as nearly alike as possible, the test results obtained will not all have the same value. A measure of the degree of agreement among these test results describes the precision of the test method for that material. Numerical measures of the variability between such test results provide inverse measures of the precision of the test method. Greater variability implies smaller (that is, poorer) precision and larger imprecision.  
4.1.2 Repeatability and Reproducibility—These two terms deal with the variability of test results obtained under specified laboratory conditions and represent the two extremes of test method precision. Repeatability concerns the variability between independent test results obtained within a single laboratory in the shortest practical period of time by a single operator with a specific set of test apparatus using test specimens (or test units) taken at random from a single quantity of homogeneous material obtained or prepared for the ILS. Reproducibility deals with the variability between single test results obtained in different laboratories, each of which has applied the test method to test specimens (or test units) taken at random from a single quantity of homogeneous material obtained or prepared for the ILS.  
4.1.2.1 Repeatability Conditions—The single-operator, single-set-of-apparatus requirement means that for a partic...
SCOPE
1.1 This practice describes the techniques for planning, conducting, analyzing, and treating the results of an interlaboratory study (ILS) of a test method. The statistical techniques described in this practice provide adequate information for formulating the precision statement of a test method.  
1.2 This practice does not concern itself with the development of test methods but rather with gathering the information needed for a test method precision statement after the development stage has been successfully completed. The data obtained 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 development of the information needed for a precision statement, the experimental design in this practice may not be optimum for evaluating materials, apparatus, or individual laboratories.  
1.4 Field of Application—This practice is concerned exclusively with test methods which yield a single numerical figure as the test result, although the single figure may be the outcome of a calculation from a set of measurements.  
1.4.1 This practice does not cover methods in which the measurement is a categorization; however, for many practical purposes categorical outcomes can be scored, such as zero-one scoring for binary measurements or as integers, ranks for example, for well-ordered categories and then the test result can be defined as an average, or other summary statistic, of several individual scores.  
1.5 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

Status
Historical
Publication Date
30-Sep-2015
ICS
19.020 - Test conditions and procedures in general
Technical Committee
E11 - Quality and Statistics
Drafting Committee
E11.20 - Test Method Evaluation and Quality Control
Current Stage
Ref Project

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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E691 − 15 AnAmerican National Standard
Standard Practice for
Conducting an Interlaboratory Study to Determine the
1
Precision of a Test Method
This standard is issued under the fixed designation E691; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript 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 2. Referenced Documents
2
1.1 This practice describes the techniques for planning, 2.1 ASTM Standards:
conducting, analyzing, and treating the results of an interlabo- E29Practice for Using Significant Digits in Test Data to
ratory study (ILS) of a test method. The statistical techniques Determine Conformance with Specifications
described in this practice provide adequate information for E177Practice for Use of the Terms Precision and Bias in
formulating the precision statement of a test method. ASTM Test Methods
E456Terminology Relating to Quality and Statistics
1.2 This practice does not concern itself with the develop-
E1169Practice for Conducting Ruggedness Tests
ment of test methods but rather with gathering the information
E1402Guide for Sampling Design
needed for a test method precision statement after the devel-
E2282Guide for Defining the Test Result of a Test Method
opment stage has been successfully completed. The data
obtained in the interlaboratory study may indicate, however,
3. Terminology
that further effort is needed to improve the test method.
3.1 Definitions—Terminology E456 provides a more exten-
1.3 Since the primary purpose of this practice is the devel-
sive list of terms in E11 standards.
opmentoftheinformationneededforaprecisionstatement,the
3.1.1 accuracy, n—the closeness of agreement between a
experimental design in this practice may not be optimum for
test result and an accepted reference value. E177
evaluating materials, apparatus, or individual laboratories.
3.1.2 bias, n—the difference between the expectation of the
1.4 Field of Application—This practice is concerned exclu-
test results and an accepted reference value. E177
sively with test methods which yield a single numerical figure
3.1.3 interlaboratory study, (ILS) in ASTM, n—a designed
asthetestresult,althoughthesinglefiguremaybetheoutcome
procedureforobtainingaprecisionstatementforatestmethod,
of a calculation from a set of measurements.
involving multiple laboratories, each generating replicate test
1.4.1 This practice does not cover methods in which the
results on one or more materials.
measurement is a categorization; however, for many practical
3.1.4 observation, n—the process of obtaining information
purposescategoricaloutcomescanbescored,suchaszero-one
regarding the presence or absence of an attribute of a test
scoring for binary measurements or as integers, ranks for
specimen, or of making a reading on a characteristic or
example, for well-ordered categories and then the test result
dimension of a test specimen. E2282
can be defined as an average, or other summary statistic, of
several individual scores.
3.1.5 precision, n—the closeness of agreements between
independent test results obtained under stipulated conditions.
1.5 This standard may involve hazardous materials,
E177
operations, and equipment. This standard does not purport to
address all of the safety problems associated with its use. It is 3.1.6 repeatability, n—precision under repeatability
the responsibility of the user of this standard to establish
conditions. E177
appropriate safety and health practices and determine the
3.1.7 repeatability conditions, n—conditions where inde-
applicability of regulatory limitations prior to use.
pendent test results are obtained with the same method on
identicaltestitemsinthesamelaboratorybythesameoperator
using the same equipment within short intervals of time. E177
1
ThispracticeisunderthejurisdictionofASTMCommitteeE11onQualityand
Statistics and is the direct responsibility of Subcommittee E11.20 on Test Method
2
Evaluation and Quality Control. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2015. Published November 2015. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1979. Last previous edition approved in 2014 as E691–14. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E0691-15. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

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E691 − 15
3.1.8 repeatability limit (r), n—
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it 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 current version
of the standard as published by ASTM is to be considered the official document.
Designation: E691 − 14 E691 − 15 An American National Standard
Standard Practice for
Conducting an Interlaboratory Study to Determine the
1
Precision of a Test Method
This standard is issued under the fixed designation E691; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript 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.
INTRODUCTION
Tests performed on presumably identical materials in presumably identical circumstances do not, in
general, yield identical results. This is attributed to unavoidable random errors inherent in every test
procedure; the factors that may influence the outcome of a test cannot all be completely controlled. In
the practical interpretation of test data, this inherent variability has to be taken into account. For
instance, the difference between a test result and some specified value may be within that which can
be expected due to unavoidable random errors, in which case a real deviation from the specified value
has not been demonstrated. Similarly, the difference between test results from two batches of material
will not indicate a fundamental quality difference if the difference is no more than can be attributed
to inherent variability in the test procedure. Many different factors (apart from random variations
between supposedly identical specimens) may contribute to the variability in application of a test
method, including: a the operator, b equipment used, c calibration of the equipment, and d
environment (temperature, humidity, air pollution, etc.). It is considered that changing laboratories
changes each of the above factors. The variability between test results obtained by different operators
or with different equipment will usually be greater than between test results obtained by a single
operator using the same equipment. The variability between test results taken over a long period of
time even by the same operator will usually be greater than that obtained over a short period of time
because 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
reference value is accuracy. To be of practical value, standard procedures are required for determining
the accuracy of a test method, both in terms of its bias and in terms of its precision. This practice
provides a standard procedure for determining the precision of a test method. Precision, when
evaluating test methods, is expressed in terms of two measurement concepts, repeatability and
reproducibility. Under repeatability conditions the factors listed above are kept or remain reasonably
constant and usually contribute only minimally to the variability. Under reproducibility conditions the
factors are generally different (that is, they change from laboratory to laboratory) and usually
contribute appreciably to the variability of test results. Thus, repeatability and reproducibility are two
practical extremes of precision.
The repeatability measure, by excluding the factors a through d as contributing variables, is not
intended as a mechanism for verifying the ability of a laboratory to maintain“ in-control” conditions
for routine operational factors such as operator-to-operator and equipment differences or any effects
of longer time intervals between test results. Such a control study is a separate issue for each
laboratory 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) reflects
what precision might be expected when random portions of a homogeneous sample are sent to random
“in-control” laboratories.
1
This practice is under the jurisdiction of ASTM Committee E11 on Quality and Statistics and is the direct responsibility of Subcommittee E11.20 on Test Method
Evaluation and Quality Control.
Current edition approved April 1, 2014Oct. 1, 2015. Published May 2014November 2015. Originally approved in 1979. Last previous edition approved in 20132014 as
E691 – 13.E691 – 14. DOI: 10.1520/E0691-14.10.1520/E0691-15.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

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SCOPE
1.1 This guide presents techniques and guidance for evaluating and assuring homogeneity of individual samples and bulk materials used for interlaboratory and intra-laboratory studies.  
1.2 This guide is applicable to samples and reference materials used for proficiency testing programs and for interlaboratory studies to determine precision estimates for test methods. It may also be useful for activities related to quality control of testing within a single laboratory.  
1.3 Five techniques are presented for assessing sample homogeneity. The five techniques are not an exhaustive list of available techniques for assessing homogeneity of samples, but the techniques were chosen to cover a range of circumstances (and various degrees of rigor required) for laboratory studies of various types and purposes.  
1.4 Each of the first four techniques provides a scheme for testing for homogeneity and a statistical procedure for evaluating the results of the homogeneity testing. The circumstances are described for which each of the techniques is suited.  
1.5 For circumstances when homogeneity testing is not possible, the fifth technique provides guidance for producing homogeneous samples.  
1.6 The appendixes of this guide provide example spreadsheets for Techniques 1, 2, 3, and 4.  
1.7 This guide is not intended for evaluation of certified reference materials (CRMs) or materials used for calibration.  
1.8 Units—The system of units for this standard is not specified. Dimensional quantities in the standard are presented only as illustrations of calculation methods. The examples are not binding on products or test methods treated.  
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to ...

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ASTM
ASTM E177-20(Practice)
Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods

ABSTRACT
The purpose of this practice is to present concepts necessary to the understanding of the terms “precision” and “bias” as used in quantitative test methods. This practice also describes methods of expressing precision and bias and, in a final section, gives examples of how statements on precision and bias may be written for ASTM test methods. A statement of precision allows potential users of a test method to assess in general terms the test method’s usefulness with respect to variability in proposed applications.
SIGNIFICANCE AND USE
4.1 Part A of the “Blue Book,” Form and Style for ASTM Standards, requires that all test methods include statements of precision and bias. This practice discusses these two concepts and provides guidance for their use in statements about test methods.  
4.2 Precision—A statement of precision allows potential users of a test method to assess in general terms the test method’s usefulness with respect to variability in proposed applications. A statement of precision is not intended to exhibit values that can be exactly duplicated in every user’s laboratory. Instead, the statement provides guidelines as to the magnitude of variability that can be expected between test results when the method is used in one, or in two or more, reasonably competent laboratories. For a discussion of precision, see 8.1.  
4.3 Bias—A statement of bias furnishes guidelines on the relationship between a set of typical test results produced by the test method under specific test conditions and a related set of accepted reference values (see 9.1).  
4.3.1 An alternative term for bias is trueness, which has a positive connotation, in that greater bias is associated with less favorable trueness. Trueness is the systematic component of accuracy.  
4.4 Accuracy—The term “accuracy,” used in earlier editions of Practice E177, embraces both precision and bias (see 9.3).
SCOPE
1.1 The purpose of this practice is to present concepts necessary to the understanding of the terms “precision” and “bias” as used in quantitative test methods. This practice also describes methods of expressing precision and bias and, in a final section, gives examples of how statements on precision and bias may be written for ASTM test methods.  
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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ASTM
ASTM E2554-18e1(Practice)
Standard Practice for Estimating and Monitoring the Uncertainty of Test Results of a Test Method Using Control Chart Techniques

ABSTRACT
This practice describes techniques for a laboratory to estimate the uncertainty of a test result using data from test results on a control sample. This practice provides one method for a laboratory to estimate Measurement Uncertainty in accordance with Section A22.3 in Form and Style for ASTM Standards. This practice describes the use of control charts to evaluate the data obtained and presents a special type of control chart to monitor the estimate of uncertainty.
This practice provides one way for a laboratory to develop data-based Type A estimates of uncertainty as referred to in Section A22 in Form and Style for ASTM Standards.
SIGNIFICANCE AND USE
4.1 This practice provides one way for a laboratory to develop data-based Type A estimates of uncertainty as referred to in Section A22 in Form and Style for ASTM Standards.  
4.2 Laboratories accredited under ISO/IEC 17025 are required to present uncertainty estimates for their test results. This practice provides procedures that use test results to develop uncertainty estimates for an individual laboratory.  
4.3 Generally, these test results will be from a single sample of stable and homogeneous material known as a control or check sample.  
4.4 The true value of the characteristic(s) of the control sample being measured will ordinarily be unknown. However, this methodology may also be used if the control sample is a reference material, in which case the test method bias may also be estimated and incorporated into the uncertainty estimate. Many test methods do not have true reference materials available to provide traceable chains of uncertainty estimation.  
4.5 This practice also allows for ongoing monitoring of the laboratory uncertainty. As estimates of the level of uncertainty change, possibly as contributions to uncertainty are identified and minimized, revision to the laboratory uncertainty will be possible.
SCOPE
1.1 This practice describes techniques for a laboratory to estimate the uncertainty of a test result using data from test results on a control sample. This practice provides one method for a laboratory to estimate Measurement Uncertainty in accordance with Section A22.3 in Form and Style for ASTM Standards.  
1.2 Uncertainty as defined by this practice applies to the capabilities of a single laboratory. Any estimate of uncertainty determined through the use of this practice applies only to the individual laboratory for which the data are presented.  
1.3 The laboratory uses a well defined and established test method in determining a series of test results. The uncertainty estimated using this practice only applies when the same test method is followed. The uncertainty only applies for the material types represented by the control samples, and multiple control samples may be needed, especially if the method has different precision for different sample types or response levels.  
1.4 The uncertainty estimate determined by this practice represents the intermediate precision of test results. This estimate seeks to quantify the total variation expected within a single laboratory using a single established test method while incorporating as many known sources of variation as possible.  
1.5 This practice does not establish error estimates (error budget) attributed to individual factors that could influence uncertainty.  
1.6 This practice describes the use of control charts to evaluate the data obtained and presents a special type of control chart to monitor the estimate of uncertainty.  
1.7 The system of units for this standard is not specified. Dimensional quantities in the standard are presented only as illustrations of calculation methods. The examples are not binding on products or test methods treated.  
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmenta...

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