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ASTM E177-20

(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

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.

General Information

Status
Published
Publication Date
30-Sep-2020
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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Standards Content (Sample)

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.
Designation: E177 − 20 An American National Standard
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 U.S. Department of Defense.
1. Scope 3. Terminology
3.1 Definitions—Terminology E456 provides a more exten-
1.1 The purpose of this practice is to present concepts
sive list of terms in E11 standards.
necessary to the understanding of the terms “precision” and
3.1.1 accepted reference value, n—a value that serves as an
“bias” as used in quantitative test methods. This practice also
agreed-upon reference for comparison, and which is derived
describes methods of expressing precision and bias and, in a
as: (1) a theoretical or established value, based on scientific
final section, gives examples of how statements on precision
principles, (2) an assigned or certified value, based on experi-
and bias may be written for ASTM test methods.
mental work of some national or international organization, or
1.2 This standard does not purport to address all of the
(3) a consensus or certified value, based on collaborative
safety concerns, if any, associated with its use. It is the
experimental work under the auspices of a scientific or
responsibility of the user of this standard to establish appro-
engineering group.
priate safety, health, and environmental practices and deter-
3.1.1.1 Discussion—A national or international
mine the applicability of regulatory limitations prior to use.
organization, referred to in 3.1.1 (2), generally maintains
measurement standards to which the reference values obtained
1.3 This international standard was developed in accor-
are traceable.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
3.1.2 accuracy, n—the closeness of agreement between a
Development of International Standards, Guides and Recom-
test result and an accepted reference value.
mendations issued by the World Trade Organization Technical
3.1.2.1 Discussion—The term accuracy, when applied to a
Barriers to Trade (TBT) Committee.
set of test results, involves a combination of a random
component and of a common systematic error or bias compo-
nent.
2. Referenced Documents
2
3.1.3 bias, n—the difference between the expectation of the
2.1 ASTM Standards:
test results and an accepted reference value.
E456 Terminology Relating to Quality and Statistics
3.1.3.1 Discussion—Bias is the total systematic error as
E691 Practice for Conducting an Interlaboratory Study to
contrasted to random error. There may be one or more
Determine the Precision of a Test Method
systematic error components contributing to the bias. A larger
E1488 GuideforStatisticalProcedurestoUseinDeveloping
systematic difference from the accepted reference value is
and Applying Test Methods
reflected by a larger bias value.
E2282 Guide for Defining the Test Result of a Test Method
3.1.4 characteristic, n—a property of items in a sample or
E2586 Practice for Calculating and Using Basic Statistics
population which, when measured, counted or otherwise
E2587 Practice for Use of Control Charts in Statistical
observed, helps to distinguish between the items. E2282
Process Control
3.1.5 coeffıcient of variation, CV, n—for a nonnegative
characteristic, the ratio of the standard deviation to the mean
for a population or sample. E2586
1
This practice is under the jurisdiction ofASTM Committee E11 on Quality and
Statistics and is the direct responsibility of Subcommittee E11.20 on Test Method
3.1.6 intermediate precision, n—precision of test results
Evaluation and Quality Control.
from tests conducted on identical material by the same test
Current edition approved Oct. 1, 2020. Published October 2020. Originally
method in a single laboratory at the same or various times with
approved in 1961. Last previous edition approved in 2019 as E177 – 19. DOI:
10.1520/E0177-20.
oneormoreknownsourcesofvariabilitycontrolledatmultiple
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
levels.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.1.6.1 Discussion—Sources of variability may include, but
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. are not limited to, operators, equ
...

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: E177 − 19 E177 − 20 An American National Standard
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 U.S. Department of Defense.
1. 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.
2. Referenced Documents
2
2.1 ASTM Standards:
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E1488 Guide for Statistical Procedures to Use in Developing and Applying Test Methods
E2282 Guide for Defining the Test Result of a Test Method
E2586 Practice for Calculating and Using Basic Statistics
E2587 Practice for Use of Control Charts in Statistical Process Control
3. Terminology
3.1 Definitions—Terminology E456 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 3.1.1 (2), generally maintains measurement standards to which the reference
values obtained are traceable.
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, 2019Oct. 1, 2020. Published December 2019October 2020. Originally approved in 1961. Last previous edition approved in 20142019
as E177 – 14.E177 – 19. DOI: 10.1520/E0177-19.10.1520/E0177-20.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’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 − 20
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. A larger 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. E2282
3.1.5 coeffıcient of variation, CV, n—for a nonnegative characteristic, the ratio of the standard deviation to t
...

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ASTM E1488-12(2023)(Guide)
Standard Guide for Statistical Procedures to Use in Developing and Applying Test Methods

ABSTRACT
This guide identifies statistical procedures for use in developing new test methods or revising or evaluating existing test methods, or both. It also cites statistical procedures especially useful in the application of test methods. This standard recommends what approaches may be taken and indicates which standards may be used to perform such assessments.
SIGNIFICANCE AND USE
4.1 The creation of a standardized test method generally follows a series of steps from inception to approval and ongoing use. In all such stages there are questions of how well the test method performs.  
4.1.1 Assessments of a new or existing test method generally involve statistical planning and analysis. This standard recommends what approaches may be taken and indicates which standards may be used to perform such assessments.  
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FIG. 1 Sequence of Steps  
4.3 All ASTM test methods are required to include statements on precision and bias.3  
4.4 Since ASTM began to require all test methods to have precision and bias statements that are based on interlaboratory test methods, there has been increased concern regarding what statistical experiments and procedures to use during the development of the test methods. Although there exists a wide range of statistical procedures, there is a small group of generally accepted techniques that are beneficial to follow. This guide is designed to provide a brief overview of these procedures and to suggest an appropriate sequence of carrying out these procedures.  
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Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

ABSTRACT
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. This practice is also 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. ASTM regulations require precision statements in all test methods in terms of repeatability and reproducibility and knowledge of the test method precision is useful in commerce and in technical work when comparing test results against standard values or between data sources.
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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 Precision is reported as a standard deviation, coefficient of variation (relative standard deviation), variance, or a precision limit (a data range indicating no statistically significant difference between test results).  
4.1.3 This practice is designed only to estimate the precision of a test method. However, when accepted reference values are available for the property levels, the test result data obtained according to this practice may be used in estimating the bias of the test method. For a discussion of bias estimation and the relationships between precision, bias, and accuracy, see Practice E177.  
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ABSTRACT
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5.2 Wipes or other cleaning equipment may be tested after use to determine the amount of contaminant removed from a surface.
Note 1: The amount of material extracted may be dependent upon the frequency and power density of the ultrasonic unit.  
5.3 The extraction efficiency has been shown to vary with the frequency and power density of the ultrasonic unit. The unit, therefore, must be carefully evaluated to optimize the extraction conditions.
SCOPE
1.1 This practice may be used to extract nonvolatile and semivolatile residues from materials such as new and used gloves, new and used wipes, component soft goods, and so forth. When used with proposed cleaning materials (wipes, gloves, and so forth), this practice may be used to determine the potential of the proposed solvent or other fluids to extract contaminants (plasticizers, residual detergents, brighteners, and so forth) and deposit them on the surface being cleaned.  
1.2 This practice is not suitable for the evaluation of particulate contamination.  
1.3 The values stated in SI units are to be regarded standard. No other units of measurement are included in this standard.  
1.4 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.  
1.5 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 D6259-23(Practice)
Standard Practice for Determination of a Pooled Limit of Quantitation for a Test Method

SIGNIFICANCE AND USE
5.1 Background—In a single laboratory, the limit of quantitation, LOQ, equal to ten times the standard deviation obtained under repeatability conditions extrapolated to zero concentration (s0) based on samples with close to zero concentrations has been recommended.3 A test result at this LOQ has an uncertainty of ±30 % at the 99 % confidence level.  
5.1.1 This practice uses a regression technique to determine a similar limit for a test method (PLOQ) using statistically pooled repeatability standard deviations over multiple operators/laboratories/samples from ILS data. This PLOQ can be used by industry to assess the reliability of a test method, or, compare reliability of different test methods, for quantitative measurement at concentrations near zero. Similarly, quantitative test results obtained using the test method for levels at or below the PLOQ can be expected by industry to have an uncertainty of ±30 % or greater at the 95 % confidence level.  
5.1.2 The regression technique described in this practice can also be used to determine a limit of quantitation specific for a single laboratory (LLOQ). The limit thus quantified for one laboratory is defined by this standard as the laboratory limit of quantitation (LLOQ).  
5.1.3 It should be noted that since differences in repeatability testing capabilities between different laboratories can exist, therefore, LLOQ determined at a single laboratory can be different than the PLOQ determined for the test method.  
5.2 Values below the PLOQ are deemed by this practice to be too uncertain for meaningful use in commerce, or in regulatory activities.
SCOPE
1.1 This practice covers the use of standard regression techniques and data from an interlaboratory study to determine a lower quantitative limit for a test method. This determined lower limit represents the numerical limit at or above which the test results are considered to be quantitatively meaningful for commerce or regulatory activities by this practice. It is defined by this standard as the pooled limit of quantitation (PLOQ) for the test method.  
1.2 This practice is applicable to test methods that are capable of producing numerical test results close to zero. Examples are those test methods that determine quantitatively the concentration of analyte(s) near zero.  
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 E2282-14(2023)(Guide)
Standard Guide for Defining the Test Result of a Test Method

ABSTRACT
The purpose of this guide is to provide guidelines for identifying the elements that comprise the test result of a test method and to illustrate how these elements combine into the test result. It covers the types of measurement scales used for expressing observations and test results. This guide provides information on the construction of test results from more elemental measurements.
SIGNIFICANCE AND USE
4.1 All test methods have an output in the form of a test result. This guide provides information on the construction of test results from more elemental measurements.  
4.2 A well defined test result is necessary before any precision statements can be made about the test method.  
4.2.1 Form and Style for ASTM Standards,2 Section A21, requires that every test method shall contain a statement regarding its precision, preferably as a result of an interlaboratory test program. Reporting of such studies is described in Practice E177, which illustrates the development of test results from observations and test determinations.  
4.2.2 Precision statements for ASTM test methods are applicable to test results. They are not applicable to test determinations or observations, unless specifically and clearly indicated otherwise.
SCOPE
1.1 The purpose of this guide is to provide guidelines for identifying the elements that comprise the test result of a test method and to illustrate how these elements combine into the test result.  
1.2 Types of measurement scales used for expressing observations and test results are discussed.  
1.3 No system of units is specified in this standard.  
1.4 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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