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ASTM E177-08

(Practice)

Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods

Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods

SIGNIFICANCE AND USE
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.
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 Section 15.
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 Section 16).  
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.  
Accuracy—The term “accuracy,” used in earlier editions of Practice E 177, embraces both precision and bias (see Section 17 and Note 3).
A Table of Contents is shown below, listing the concepts in this standard. TABLE OF CONTENTSSection  GENERAL CONCEPTS Test Method 5  Measurement Terminology 6   SOURCES OF VARIABILITY Experimental Realization of a Test Method 7 Operator 8  Apparatus 9  Environment 10  Sample 11  Time 12   STATISTICAL CONCEPTS Accepted Reference Value 13  Statistical Control 14  Precision 15  Bias 16  Accuracy 17  Variation of Precision and Bias with Material 18  Variation of Precision and Bias with Sources of Variability 19   COMBINATIONS OF SOURCES OF VARIABILITY Repeatability and Laboratory Bias 20  Other Within-a-Single Laboratory Prec...
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 and health practices and determine the applicability of regulatory requirements prior to use.

General Information

Status
Historical
Publication Date
30-Sep-2008
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

Relations

Replaces
ASTM E177-06b - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
Effective Date
01-Oct-2008
Replaced By
ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
Effective Date
01-Oct-2010
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Standards Content (Sample)

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
An American National Standard
Designation:E177–08
Standard Practice for
1
Use of the Terms Precision and Bias in ASTM Test Methods
This standard is issued under the fixed designation E177; 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 Department of Defense.
1. Scope 3.1.1.1 Discussion—A national or international organiza-
tion, referred to in 3.1.1 (2), generally maintains measurement
1.1 The purpose of this practice is to present concepts
standards to which the reference values obtained are traceable.
necessary to the understanding of the terms “precision” and
3.1.2 accuracy, n—the closeness of agreement between a
“bias” as used in quantitative test methods. This practice also
test result and an accepted reference value.
describes methods of expressing precision and bias and, in a
3.1.2.1 Discussion—The term accuracy, when applied to a
final section, gives examples of how statements on precision
set of test results, involves a combination of a random
and bias may be written for ASTM test methods.
component and of a common systematic error or bias compo-
1.2 This standard does not purport to address all of the
nent.
safety concerns, if any, associated with its use. It is the
3.1.3 bias, n—the difference between the expectation of the
responsibility of the user of this standard to establish appro-
test results and an accepted reference value.
priate safety and health practices and determine the applica-
3.1.3.1 Discussion—Bias is the total systematic error as
bility of regulatory requirements prior to use.
contrasted to random error. There may be one or more
2. Referenced Documents systematic error components contributing to the bias. A larger
2
systematic difference from the accepted reference value is
2.1 ASTM Standards:
reflected by a larger bias value.
E178 Practice for Dealing With Outlying Observations
3.1.4 characteristic, n—a property of items in a sample or
E456 Terminology Relating to Quality and Statistics
population which, when measured, counted or otherwise ob-
E691 Practice for Conducting an Interlaboratory Study to
served, helps to distinguish between the items. E2282
Determine the Precision of a Test Method
3.1.5 intermediate precision, n—the closeness of agreement
E2282 Guide for Defining the Test Result of a Test Method
between test results obtained under specified intermediate
3. Terminology
precision conditions.
3.1.5.1 Discussion—The specific measure and the specific
3.1 Definitions: Terminology E456 provides a more exten-
conditions must be specified for each intermediate measure of
sive list of terms in E11 standards.
precision; thus, “standard deviation of test results among
3.1.1 accepted reference value, n—a value that serves as an
operators in a laboratory,” or “day-to-day standard deviation
agreed-upon reference for comparison, and which is derived
within a laboratory for the same operator.”
as: (1) a theoretical or established value, based on scientific
3.1.5.2 Discussion—Because the training of operators, the
principles, (2) an assigned or certified value, based on experi-
agreement of different pieces of equipment in the same
mental work of some national or international organization, or
laboratory and the variation of environmental conditions with
(3) a consensus or certified value, based on collaborative
longer time intervals all depend on the degree of within-
experimental work under the auspices of a scientific or
laboratory control, the intermediate measures of precision are
engineering group.
likely to vary appreciably from laboratory to laboratory. Thus,
intermediate precisions may be more characteristic of indi-
1
This practice is under the jurisdiction ofASTM Committee E11 on Quality and
vidual laboratories than of the test method.
Statistics and is the direct responsibility of Subcommittee E11.20 on Test Method
3.1.6 intermediate precision conditions, n—conditions un-
Evaluation and Quality Control.
der which test results are obtained with the same test method
Current edition approved Oct. 1, 2008. Published October 2008. Originally
approved in 1961. Last previous edition approved in 2006 as E177 – 06b. DOI:
usingtestunitsortestspecimenstakenatrandomfromasingle
10.1520/E0177-08.
quantity of material that is as nearly homogeneous as possible,
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and with changing conditions such as operator, measuring
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summa
...

This document is not anASTM standard and is intended only to provide the user of anASTM 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.
An American National Standard
Designation:E177–06b Designation:E177–08
Standard Practice for
1
Use of the Terms Precision and Bias in ASTM Test Methods
This standard is issued under the fixed designation E 177; 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 Department of Defense.
1. Scope
1.1 Thepurposeofthispracticeistopresentconceptsnecessarytotheunderstandingoftheterms“precision”and“bias”asused
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 and health practices and determine the applicability of regulatory
requirements prior to use.
2. Referenced Documents
2
2.1 ASTM Standards:
E 178 Practice for Dealing With Outlying Observations
E 456 Terminology Relating to Quality and Statistics
E 691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E 2282 Guide for Defining the Test Result of a Test Method
3. Terminology
3.1 Definitions: Terminology E 456 provides a more extensive list of terms in E11 standards.
3.1.1 accepted reference value, n—a value that serves as an agreed-upon reference for comparison, and which is derived as: (1)
a theoretical or established value, based on scientific principles, (2) an assigned or certified value, based on experimental work of
some national or international organization, or (3) a consensus or certified value, based on collaborative experimental work under
the auspices of a scientific or engineering group.
3.1.1.1 Discussion—A national or international organization, referred to in (2), generally maintains measurement standards to
which the reference values obtained are traceable.
3.1.2 accuracy, n—the closeness of agreement between a test result and an accepted reference value.
3.1.2.1 Discussion—The term accuracy, when applied to a set of test results, involves a combination of a random component
and of a common systematic error or bias component.
3.1.3 bias, n—the difference between the expectation of the test results and an accepted reference value.
3.1.3.1 Discussion—Bias is the total systematic error as contrasted to random error.There may be one or more systematic error
components contributing to the bias.Alarger systematic difference from the accepted reference value is reflected by a larger bias
value.
3.1.4 characteristic, n—a property of items in a sample or population which, when measured, counted or otherwise observed,
helps to distinguish between the items. E 2282
3.1.5 intermediateprecision,n—theclosenessofagreementbetweentestresultsobtainedunderspecifiedintermediateprecision
conditions.
3.1.4.1
3.1.5.1 Discussion—The specific measure and the specific conditions must be specified for each intermediate measure of
precision; thus, “standard deviation of test results among operators in a laboratory,” or “day-to-day standard deviation within a
laboratory for the same operator.”
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 Nov. 15, 2006.Oct. 1, 2008. Published January 2007.October 2008. Originally approved in 1961. Last previous edition approved in 2006 as
E 177 – 06ab.
2
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book ofASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1

---------------------- Page: 1 ----------------------
E177–08
3.1.4.2
3.1.5.2 Discussion—Because the training of operators, the agreement of different pieces of equipment in the same laboratory
and the variation of environmental conditions with longer time intervals all depend on the degree of within-laboratory control, the
intermediate measures
...

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Standard Terminology Relating to Design of Experiments

ABSTRACT
This standard includes those statistical items related to the area of design of experiments for which standard definitions appear desirable. It provides definitions, descriptions, discussion, and comparison of terms.
SIGNIFICANCE AND USE
3.1 This standard is a subsidiary to Terminology E456.  
3.2 It provides definitions, descriptions, discussion, and comparison of terms.
SCOPE
1.1 This standard includes those statistical items related to the area of design of experiments for which standard definitions appear desirable.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
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 E3264-21(Guide)
Standard Guide for Homogeneity of Samples and Reference Materials Used for Inter- and Intra-Laboratory Studies

SIGNIFICANCE AND USE
5.1 This guide presents techniques and guidance for evaluating and assuring homogeneity of individual samples or bulk materials and can be used for either interlaboratory or intra-laboratory studies. The types of studies include, but are not limited to, studies to determine precision estimates for test methods, proficiency testing programs, and studies related to quality control of testing within a single laboratory.  
5.2 Because the test results of any laboratory study are affected by the quality of the samples tested, producing homogeneous samples and determining the degree of homogeneity is important for interpreting the results of the study.  
5.3 Five techniques are presented in this guide to evaluate sample homogeneity for a range of circumstances and degrees of rigor. The circumstances under which the studies are conducted and the degree of rigor required may differ. The user should consider the circumstances listed in each technique to determine which is appropriate for the study at hand.  
5.4 Each of the Techniques 1, 2, and 3 provides a procedure for testing and evaluating sample homogeneity when replicate testing of the samples is possible. Technique 4 provides a plan to evaluate sample homogeneity when replicate testing is not possible. Technique 5 recommends practices for producing homogeneous samples for circumstances when homogeneity testing is not possible.  
5.5 When the conditions of adequate within-sample homogeneity and between-sample homogeneity are satisfied, any differences in test results on multiple samples can reasonably be attributed to testing variation and not due to sample variation.  
5.6 When differences within or between samples are discovered and the samples are deemed insufficiently homogeneous, the sample preparation process can be improved or corrected and a new set of samples can be prepared. Or, in cases where the sample homogeneity cannot be improved or for other reasons when the samples must be used, the method of eval...
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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