ASTM E177-20

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

Relations

• Refers: ASTM E2282-23 - Standard Guide for Defining the Test Result of a Test Method
• Effective Date: 01-Nov-2023
• Refers: ASTM E1488-23 - Standard Guide for Statistical Procedures to Use in Developing and Applying Test Methods
• Effective Date: 01-Nov-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E2586-19e1 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Apr-2019
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E2587-15 - Standard Practice for Use of Control Charts in Statistical Process Control
• Effective Date: 01-Apr-2015
• Refers: ASTM E2587-14 - Standard Practice for Use of Control Charts in Statistical Process Control
• Effective Date: 01-Oct-2014
• Refers: ASTM E2587-14e1 - Standard Practice for Use of Control Charts in Statistical Process Control
• Effective Date: 01-Oct-2014
• Refers: ASTM E2282-14 - Standard Guide for Defining the Test Result of a Test Method
• Effective Date: 01-Oct-2014
• Refers: ASTM E2586-14 - Standard Practice for Calculating and Using Basic Statistics
• Effective Date: 01-Jun-2014
• Refers: ASTM E456-13ae1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13a - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae2 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013
• Refers: ASTM E456-13ae3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 15-Nov-2013

Overview

ASTM E177-20: Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods is a foundational guideline published by ASTM International. This standard provides critical definitions and practices related to the terms “precision” and “bias” as they are applied in quantitative test methods. ASTM E177-20 also outlines methods for expressing precision and bias in laboratory and interlaboratory testing, helping ensure clarity, consistency, and reliability in ASTM test methods.

By offering a unified understanding and approach to these terms, this standard assists test method developers, laboratory managers, and quality professionals in properly evaluating and conveying the reliability and relevance of test results.

Key Topics

ASTM E177-20 addresses several key concepts relevant to quality assurance in testing:

• Precision: Focuses on the closeness of agreement between independent test results under prescribed conditions. This includes:

  • Repeatability: Precision within a single laboratory with the same operator and equipment over a short period.
  • Reproducibility: Precision across different laboratories, operators, and equipment.
  • Intermediate Precision: Precision considering variations such as different days or operators within the same laboratory.

• Bias: Explains the difference between the average result of a test method and an accepted reference value. Bias is often addressed through comparison with certified reference materials and documented reference values.

• Accuracy: Although not recommended as a standalone descriptor, accuracy is explained as a combination of precision and bias.

• Statements of Precision and Bias: Guidance on how to properly document and communicate these aspects in ASTM test methods for users’ reference.

• Sources of Variability: Details factors affecting test results, such as operator technique, equipment calibration, environmental conditions, specimen sampling, and time.

Applications

ASTM E177-20 finds practical value in a variety of applications related to laboratory testing, method development, and quality management:

• Test Method Development: Ensures that new quantitative test methods include clear, standardized statements of precision and bias, which are essential for regulatory compliance and industry acceptance.
• Quality Control: Laboratories can assess and improve the variability of their test methods, ensuring consistent results within and between facilities.
• Interlaboratory Studies: Facilitates the design and interpretation of interlaboratory comparison studies, which are critical for establishing reproducibility and method robustness.
• Regulatory Reporting: Supplies clear definitions and methods for reporting precision and bias, improving the quality of data in compliance, accreditation, and certification processes.
• Training and Documentation: Serves as a reference to educate laboratory staff and ensure adherence to globally recognized measurement terminology and practices.

Related Standards

For comprehensive implementation and compatibility with quality and statistical practices, reference these ASTM standards frequently cited alongside ASTM E177-20:

• ASTM E456 - Terminology Relating to Quality and Statistics
• ASTM E691 - Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• ASTM E1488 - Guide for Statistical Procedures to Use in Developing and Applying Test Methods
• ASTM E2282 - Guide for Defining the Test Result of a Test Method
• ASTM E2586 - Practice for Calculating and Using Basic Statistics
• ASTM E2587 - Practice for Use of Control Charts in Statistical Process Control

Keywords: ASTM E177-20, precision, bias, test method validity, laboratory quality control, reproducibility, repeatability, measurement terminology, interlaboratory studies, quality assurance, ASTM standards.

By following ASTM E177-20, organizations ensure that their test methods provide transparent, reliable, and internationally consistent information about the quality and comparability of measurement results.

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
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
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
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
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
levels.
contact ASTM Customer Service at [e-mail]. 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, equipment, instruments, reagents,
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E177 − 20
environment, or the length of the time period over which the but are not limited to, operators, equipment, instruments,
testing was conducted. reagents, or environment.
3.1.6.2 Discussion—The specific measure and the specific
3.1.13 repeatability conditions, n—conditions where inde-
conditions must be specified for each intermediate measure of
pendent test results are obtained with the same method on
precision; thus, “standard deviation of test results among
identical test items in the same laboratory by the same operator
operators in a laboratory,” or “day-to-day standard deviation
using the same equipment within short intervals of time.
within a laboratory for the same operator.”
3.1.13.1 Discussion—See precision, The “same operator,
3.1.6.3 Discussion—Because the training of operators, the
same equipment” requirement means that for a particular step
agreement of different pieces of equipment in the same
in the measurement process, the same combination of operator
laboratory and the variation of environmental conditions with
and equipment is used for every test result. Thus, one operator
longer time intervals all depend on the degree of within-
may prepare the test specimens, a second measure the dimen-
laboratory control, the intermediate measures of precision are
sions and a third measure the mass in a test method for
likely to vary appreciably from laboratory to laboratory. Thus,
determining density.
intermediate precisions may be more characteristic of indi-
3.1.13.2 Discussion—By “in the shortest practical period of
vidual laboratories than of the test method.
time” is meant that the test results, at least for one material, are
3.1.7 intermediate precision conditions, n—conditions un-
obtainedinatimeperiodnotlessthaninnormaltestingandnot
der which test results are obtained with the same test method
so long as to permit significant change in test material,
usingtestunitsortestspecimenstakenatrandomfromasingle
equipment or environment.
quantity of material that is as nearly homogeneous as possible,
3.1.14 repeatability limit (r), n—the value below which the
and with changing conditions such as operator, measuring
absolutedifferencebetweentwoindividualtestresultsobtained
equipment, location within the laboratory, and time.
under repeatability conditions may be expected to occur with a
3.1.8 laboratory precision, n—the precision of test results
probability of approximately 0.95 (95 %).
obtained within a laboratory for identical material under
3.1.14.1 Discussion—The repeatability limit is
conditions that include all known sources of variation within
~ = !
2.8 '1.96 2 times the repeatability standard deviation. This
the laboratory over extended periods of time, often months.
multiplier is independent of the size of the interlaboratory
3.1.8.1 Discussion—Laboratory precision is also known as
study.
site precision.
3.1.14.2 Discussion—The approximation to 0.95 is reason-
3.1.9 observation, n—the process of obtaining information
ably good (say 0.90 to 0.98) when many laboratories (30 or
regarding the presence or absence of an attribute of a test
more) are involved, but is likely to be poor when fewer than
specimen, or of making a reading on a characteristic or
eight laboratories are studied.
dimension of a test specimen. E2282
3.1.15 repeatability standard deviation (s ), n—the standard
3.1.10 observed value, n—the value obtained by making an r
deviation of test results obtained under repeatability condi-
observation. E2282
tions.
3.1.11 precision, n—the closeness of agreement between
3.1.15.1 Discussion—It is a measure of the dispersion of the
independent test results obtained under stipulated conditions.
distribution of test results under repeatability conditions.
3.1.11.1 Discussion—Precision depends on random errors
3.1.15.2 Discussion—Similarly, “repeatability variance”
and does not relate to the accepted reference value.
and“repeatabilitycoefficientofvariation”couldbedefinedand
3.1.11.2 Discussion—The measure of precision usually is
used as measures of the dispersion of test results under
expressed in terms of imprecision and computed as a standard
repeatability conditions. In an interlaboratory study, this is the
deviation of the test results. Less precision is reflected by a
pooled standard deviation of test results obtained under repeat-
larger standard deviation.
ability conditions.
3.1.11.3 Discussion—“Independent test results” means re-
3.1.16 reproducibility, n—precision of test results from tests
sults obtained in a manner not influenced by any previous
conducted on identical material by the same test method in
result on the same or similar test object. Quantitative measures
different laboratories (see reproducibility conditions).
of precision depend critically on the stipulated conditions.
3.1.16.1 Discussion—All sources of known variability are
Repeatability and reproducibility conditions are particular sets
of extreme stipulated conditions. involvedbecauseofthedifferentsourcesofvariationoccurring
between laboratories.
3.1.12 repeatability, n—precision of test results from tests
conducted within the shortest practical time period on identical 3.1.17 reproducibility conditions, n—conditions where test
material by the same test method in a single laboratory with all results are obtained with the same method on identical test
items in different laboratories with different operators using
known sources of variability conditions controlled at the same
levels (see repeatability conditions). different equipment.
3.1.12.1 Discussion—Repeatabilityisoneoftheconceptsor 3.1.17.1 Discussion—Identical material means either the
categories of the precision of a test method. Measures of
same test units or test specimens are tested by all the
repeatability defined in this compilation are repeatability stan- laboratories as for a nondestructive test or test units or test
dard deviation and repeatability limit.
specimens are taken at random from a single quantity of
3.1.12.2 Discussion—Sources of variability may include, material that is as nearly homogeneous as possible.
E177 − 20
A different laboratory of necessity means a different 4. Significance and Use
operator, different equipment, and different location and
4.1 Part A of the “Blue Book,” Form and Style for ASTM
under different supervisory control.
Standards, requires that all test methods include statements of
3.1.18 reproducibility limit (R), n—the value below which
precision and bias. This practice discusses these two concepts
the absolute difference between two test results obtained under
and provides guidance for their use in statements about test
reproducibility conditions may be expected to occur with a
methods.
probability of approximately 0.95 (95 %).
4.2 Precision—A statement of precision allows potential
3.1.18.1 Discussion—The reproducibility limit is
users of a test method to assess in general terms the test
2.8 ~'1.96 =2! times the reproducibility standard deviation.
method’s usefulness with respect to variability in proposed
The multiplier is independent of the size of the interlaboratory
applications.Astatement of precision is not intended to exhibit
study (that is, of the number of laboratories participating).
valuesthatcanbeexactlyduplicatedineveryuser’slaboratory.
3.1.18.2 Discussion—The approximation to 0.95 is reason- Instead, the statement provides guidelines as to the magnitude
ably good (say 0.90 to 0.98) when many laboratories (30 or
of variability that can be expected between test results when
more) are involved but is likely to be poor when fewer than
the method is used in one, or in two or more, reasonably
eight laboratories are studied.
competent laboratories. For a discussion of precision, see 8.1.
3.1.19 reproducibility standard deviation (s ), n—the stan-
R 4.3 Bias—A statement of bias furnishes guidelines on the
dard deviation of test results obtained under reproducibility
relationship between a set of typical test results produced by
conditions.
the test method under specific test conditions and a related set
3.1.19.1 Discussion—Other measures of the dispersion of
of accepted reference values (see 9.1).
test results obtained under reproducibility conditions are the
4.3.1 An alternative term for bias is trueness, which has a
“reproducibility variance” and the “reproducibility coefficient
positive connotation, in that greater bias is associated with less
of variation.”
favorable trueness. Trueness is the systematic component of
3.1.19.2 Discussion—The reproducibility standard devia-
accuracy.
tion includes, in addition to between-laboratory variability, the
4.4 Accuracy—The term “accuracy,” used in earlier editions
repeatability standard deviation and a contribution from the
of Practice E177, embraces both precision and bias (see 9.3).
interaction of laboratory factors (that is, differences between
operators, equipment and environments) with material factors
5. Test Method
(that is, the differences between properties of the materials
other than that property of interest).
5.1 Section 2 of the ASTM Regulations describes a test
3.1.20 standard deviation, n—of a population,σ,thesquare
method as “a definitive procedure for the identification,
root of the average or expected value of the squared deviation measurement, and evaluation of one or more qualities,
of a variable from its mean; —of a sample, s, the square root
characteristics, or properties of a material, product, system or
of the sum of the squared deviations of the observed values in
service that produces a test result.”
the sample divided by the sample size minus 1. E2586
5.2 In this practice only quantitative test methods that
3.1.21 test determination, n—the value of a characteristic or
produce numerical results are considered. Also, the word
dimension of a single test specimen derived from one or more
“material”isusedtomeanmaterial,product,systemorservice;
observed values. E2282
the word “property” is used herein to mean that a quantitative
test result can be obtained that describes a characteristic or a
3.1.22 test method, n—a definitive procedure that produces
quality, or some other aspect of the material; and “test method”
a test result. E2282
refers to both the document and the procedure described
3.1.23 test result, n—the value of a characteristic obtained
therein for obtaining a quantitative test result for one property.
by carrying out a specified test method. E2282
For a discussion of test result, see 7.1.
3.1.24 test specimen, n—the portion of a test unit needed to
5.3 A well-written test method specifies control over such
obtain a single test determination. E2282
factors as the test equipment, the test environment, the quali-
3.1.25 test unit, n—the total quantity of material (containing
fications of the operator (explicitly or implicitly), the prepara-
one or more test specimens) needed to obtain a test result as
tion of test specimens, and the operating procedure for using
specified in the test method. See test result. E2282
the equipment in the test environment to measure some
property of the test specimens. The test method will also
3.1.26 trueness, n—the closeness of agreement between the
specify the number of test specimens required and how
population mean of the measurements or test results and the
accepted reference value. measurements on them are to be combined to provide a test
result (7.1), and might also reference a sampling procedure
3.1.26.1 Discussion—“Population mean” is, conceptually,
appropriate for the intended use of the method.
the average value of an indefinitely large number of test results
2 2
5.4 Itisnecessarythatthewritersofthetestmethodprovide
3.1.27 variance,σ ,s ,n— square of the standard deviation
of the population or sample. E2586 instructionsorrequirementsforeveryknownoutsideinfluence.
E177 − 20
5.5 Atest method conducted in a laboratory should demon- potential sources of variability. Some of the more common
strate a long-term state of statistical control (see Refs. (1-3), factors are discussed in 7.2 – 7.6.
Guide E1488, and Practice E2587).
7.2 Operator:
7.2.1 Clarity of Test Method—Every effort must be made in
6. Measurement Terminology
preparing an ASTM standard test method to eliminate the
6.1 A test result is the value obtained by carrying out the
possibility of serious differences in interpretation. One way to
complete protocol of the test method once, being as simple as
check clarity is to observe, without comment, a competent
the result of a single direct visual observation on a test
laboratory operator, not previously familiar with the method,
specimen or the result of a complex series of automated
apply the draft test method. If the operator has any difficulty,
procedures with the test result calculation performed by a
the draft most likely needs revision.
computer.
7.2.2 Completeness of Test Method—It is necessary that
6.2 The following terms are used to describe partial results
operators, who are generally familiar with the test method or
of the test method: observed value, and test determination,
similar methods, not read anything into the instructions that is
which are more fully described in Guide E2282.
not explicitly stated therein. Therefore, to ensure minimum
6.2.1 An observed valueisinterpretedasthemostelemental
variability due to interpretation, procedural requirements must
single reading obtained in the process of making an observa-
be complete.
tion.As examples, an observation may involve a zero-adjusted
7.2.2.1 If requirements are not explicitly stated in the test
micrometer reading of the thickness of a test strip at one
method (see 5.4), they must be included in the instructions for
position along the strip or the weight of a subsample taken
the interlaboratory study (see Practice E691).
from a powder sample.
7.2.3 Differences in Operator Technique—Even when op-
6.2.2 A test determination summarizes or combines one or
erators have been trained by the same instructor or supervisor
more observed values. For example, (1) the measurement of
to give practically identical interpretations to the various steps
the bulk density of a powder may involve the observation of
of the test method, different operators (or even the same
the mass and the tamped volume of the sample specimen, and
operator at different times) may still differ in such things as
the calculated bulk density as the ratio mass/volume is a test
dexterity, reaction time, color sensitivity, interpolation in scale
determination; (2) the test determination of the thickness of a
reading, and so forth. Unavoidable operator differences are
test specimen strip may involve averaging micrometer caliper
thus one source of variability between test results. The test
observations taken at several points along the strip.
method should be designed and described to minimize the
6.2.3 Atest result summarizes or combines one or more test
effects of these operator sources of variability.
determinations. For example, (1) a test method on bulk density
7.3 Apparatus:
might require that the test determination of density for each of
7.3.1 Tolerances—In order to avoid prohibitive costs, only
five subsamples of the powder sample be averaged to calculate
necessary and reasonable manufacturing and maintenance
the test result; (2) a test method may involve multiple auto-
tolerances can be specified. The variations allowed by these
mated operations, combined with a calibration procedure, with
reasonable specification tolerances can be one source of
many observed values and test determinations, and the test
variability between test results from different sets of test
result calculated and printed out by a computer.
equipment.
6.3 Precision statements for ASTM test methods are appli-
7.3.2 Calibration—One of the variables associated with the
cable to comparisons between test results, not test determina-
equipment is its state of calibration, including traceability to
tions nor observations, unless specifically and clearly indicated
national standards. The test method must provide guidance on
otherwise.
the frequency of verification and of partial or complete
7. Sources of Variability recalibration; that is, for each test determination, each test
result, once a day, week, etc., or as required in specified
7.1 Sources of Variation of Test Results:
situations.Calibrationdriftintroducesbiasintotestresultsover
7.1.1 Generation of a test result involves an interpretation
time. However, frequent unnecessary calibration contributes to
of the written document by an operator, who uses a specific
variability of test results.
unit and version of the specified test apparatus,inthe particu-
lar environment of this testing laboratory, to evaluate a 7.4 Environment:
specified number of test specimens of the material to be tested.
7.4.1 The properties of many materials are sensitive to
Replicate test results will differ due to changes in one or more
temperature, humidity, atmospheric pressure, atmospheric
of the above emphasized experimental factors. Even when
contaminants, and other environmental factors. The test
noneoftheexperimentalfactorsisintentionallychanged,small
method usually specifies the standard environmental condi-
changes usually occur. The outcome of these changes may be
tions for testing. However, since these factors cannot be
seen as variability among the test results.
controlled perfectly within and between laboratories, a test
7.1.2 Each of the above experimental factors and all others,
method must be able to cope with a reasonable amount of
known and unknown, that can change the test result, are
variabilitythatinevitablyoccurseventhoughmeasurementand
adjustment for the environmental variation have been used to
obtaincontrol(see5.5).Thus,themethodmustberobusttothe
The boldface numbers in parentheses refer to a list of references at the end of
this standard. differences between laboratories.
E177 − 20
7.5 Sample (Test Specimens): 8.1.3 Two conditions applicable to ASTM test methods are
repeatability conditions and reproducibility conditions, and
7.5.1 Alot(orshipment)ofmaterialmustbesampled.Since
these lead to estimates of the repeatability and reproducibility
it is unlikely that the material is perfectly uniform, sampling
of a test method. Other conditions can be defined and are
variabilityisanothersourceofvariabilityamongtestresults.In
known collectively as intermediate precision conditions. The
some applications, useful interpretation of test results may
long run variability within one laboratory is an intermediate
require the measurement of the sampling error. In interlabora-
precision condition of particular importance (see 8.4.2).
tory evaluation of test methods to determine testing variability,
special attention is required in the selection of the material
8.2 Repeatability:
sample (see 10.3.4 and Practice E691) in order to obtain test
8.2.1 Repeatability is precision determined from multiple
specimens that are as similar as possible. A small residual
test results conducted under repeatability conditions, where the
amount of material variability is almost always an inseparable
test method is conducted by a single, well-trained operator
component of any estimate of testing variability.
using one set of equipment in a short period of time during
7.5.2 Handling and size reduction of material during sam-
which neither the equipment nor the environment is likely to
pling can affect the test result when involving exposure to heat,
change appreciably. Any variability is due to small changes in
light, and the atmosphere. Testing of unstable materials re-
conducting the test operations and possible variation of the
quires attention to all aspects of the measurement operation,
measured property among test samples. The latter is kept to a
not just the test method itself, to control both systematic error
minimum by use of proper sampling procedures in test sample
and variability.
preparation. All potential sources of variability must be care-
fully controlled within the tolerances specified in the test
7.6 Time:
method.
7.6.1 Each of the above sources of variability (operator
performance, equipment, environment, test specimens) may NOTE 1—If the test method requires a series of steps, the “single-
operator-equipment”requirementmeansthatforaparticularstepthesame
change with time; for example, during a period when two or
combination of operator and equipment is used for every test result and on
more test results are obtained. The longer the period, the less
every material. Thus one operator may prepare the test specimens, a
likely changes in these sources will remain random (that is, the
second measure the dimensions and a third measure the breaking force.
more likely systematic effects will enter), thereby increasing
The “single-day” requirement means that the test results, at least for a
the net change and the observed differences in test results. particular material are obtained in the shortest practical period of time,
whether this be a fraction of a day or several days.
These differences will also depend on the degree of control
exercised within the laboratory over the sources of variability.
8.2.2 The repeatability precision may be estimated in a
In conducting an interlaboratory evaluation of a test method,
single experiment in a laboratory as the standard deviation of
thetimespanoverwhichthemeasurementsaremadeshouldbe
the test results obtained under repeatability conditions. The
kept as short as reasonably possible (see 8.2.4).
number of test results should be recorded along with the
standard deviation estimate.
8. Precision
8.2.3 An estimate of repeatability may also be provided by
multiple experiments in the same laboratory over time, each
8.1 Precision:
experiment being conducted under repeatability conditions.
8.1.1 The precision of a measurement process, and hence
The pooled standard deviation is calculated and used as the
the stated precision of the test method from which the process
estimate of the long term repeatability for that laboratory,
is generated, is a generic concept related to the closeness of
termed the laboratory repeatability.
agreement between test results obtained under prescribed
8.2.4 A repeatability estimate for a test method may be
conditions from the measurement process being evaluated.The
provided
...

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
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
2.1 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.
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.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
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 the mean for a
population or sample. E2586
3.1.6 intermediate precision, n—precision of test results from tests conducted on identical material by the same test method in a
single laboratory at the same or various times with one or more known sources of variability controlled at multiple levels.
3.1.6.1 Discussion—
Sources of variability may include, but are not limited to, operators, equipment, instruments, reagents, environment, or the length
of the time period over which the testing was conducted.
3.1.6.2 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.”
3.1.6.3 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 of precision are likely to vary appreciably from laboratory to laboratory. Thus, intermediate precisions may be more
characteristic of individual laboratories than of the test method.
3.1.7 intermediate precision conditions, n—conditions under which test results are obtained with the same test method using test
units or test specimens taken at random from a single quantity of material that is as nearly homogeneous as possible, and with
changing conditions such as operator, measuring equipment, location within the laboratory, and time.
3.1.8 laboratory precision, n—the precision of test results obtained within a laboratory for identical material under conditions that
include all known sources of variation within the laboratory over extended periods of time, often months.
3.1.8.1 Discussion—
Laboratory precision is also known as site precision.
3.1.9 observation, n—the process of obtaining information regarding the presence or absence of an attribute of a test specimen,
or of making a reading on a characteristic or dimension of a test specimen. E2282
3.1.10 observed value, n—the value obtained by making an observation. E2282
3.1.11 precision, n—the closeness of agreement between independent test results obtained under stipulated conditions.
3.1.11.1 Discussion—
Precision depends on random errors and does not relate to the accepted reference value.
3.1.11.2 Discussion—
The measure of precision usually is expressed in terms of imprecision and computed as a standard deviation of the test results. Less
precision is reflected by a larger standard deviation.
3.1.11.3 Discussion—
“Independent test results” means results obtained in a manner not influenced by any previous result on the same or similar test
object. Quantitative measures of precision depend critically on the stipulated conditions. Repeatability and reproducibility
conditions are particular sets of extreme stipulated conditions.
E177 − 20
3.1.12 repeatability, n—precision of test results from tests conducted within the shortest practical time period on identical material
by the same test method in a single laboratory with all known sources of variability conditions controlled at the same levels (see
repeatability conditions).
3.1.12.1 Discussion—
Repeatability is one of the concepts or categories of the precision of a test method. Measures of repeatability defined in this
compilation are repeatability standard deviation and repeatability limit.
3.1.12.2 Discussion—
Sources of variability may include, but are not limited to, operators, equipment, instruments, reagents, or environment.
3.1.13 repeatability conditions, n—conditions where independent test results are obtained with the same method on identical test
items in the same laboratory by the same operator using the same equipment within short intervals of time.
3.1.13.1 Discussion—
See precision, The “same operator, same equipment” requirement means that for a particular step in the measurement process, the
same combination of operator and equipment is used for every test result. Thus, one operator may prepare the test specimens, a
second measure the dimensions and a third measure the mass in a test method for determining density.
3.1.13.2 Discussion—
By “in the shortest practical period of time” is meant that the test results, at least for one material, are obtained in a time period
not less than in normal testing and not so long as to permit significant change in test material, equipment or environment.
3.1.14 repeatability limit (r), n—the value below which the absolute difference between two individual test results obtained under
repeatability conditions may be expected to occur with a probability of approximately 0.95 (95 %).
3.1.14.1 Discussion—
The repeatability limit is
~ = !
2.8 '1.96 2 times the repeatability standard deviation. This multiplier is independent of the size of the interlaboratory study.
3.1.14.2 Discussion—
The approximation to 0.95 is reasonably good (say 0.90 to 0.98) when many laboratories (30 or more) are involved, but is likely
to be poor when fewer than eight laboratories are studied.
3.1.15 repeatability standard deviation (s ), n—the standard deviation of test results obtained under repeatability conditions.
r
3.1.15.1 Discussion—
It is a measure of the dispersion of the distribution of test results under repeatability conditions.
3.1.15.2 Discussion—
Similarly, “repeatability variance” and “repeatability coefficient of variation” could be defined and used as measures of the
dispersion of test results under repeatability conditions. In an interlaboratory study, this is the pooled standard deviation of test
results obtained under repeatability conditions.
3.1.16 reproducibility, n—precision of test results from tests conducted on identical material by the same test method in different
laboratories (see reproducibility conditions).
3.1.16.1 Discussion—
All sources of known variability are involved because of the different sources of variation occurring between laboratories.
3.1.17 reproducibility conditions, n—conditions where test results are obtained with the same method on identical test items in
different laboratories with different operators using different equipment.
3.1.17.1 Discussion—
Identical material means either the same test units or test specimens are tested by all the laboratories as for a nondestructive test
or test units or test specimens are taken at random from a single quantity of material that is as nearly homogeneous as possible.
A different laboratory of necessity means a different operator, different equipment, and different location and under different
supervisory control.
3.1.18 reproducibility limit (R), n—the value below which the absolute difference between two test results obtained under
reproducibility conditions may be expected to occur with a probability of approximately 0.95 (95 %).
3.1.18.1 Discussion—
The reproducibility limit is
E177 − 20
2.8 ~'1.96 =2! times the reproducibility standard deviation. The multiplier is independent of the size of the interlaboratory study
(that is, of the number of laboratories participating).
3.1.18.2 Discussion—
The approximation to 0.95 is reasonably good (say 0.90 to 0.98) when many laboratories (30 or more) are involved but is likely
to be poor when fewer than eight laboratories are studied.
3.1.19 reproducibility standard deviation (s ), n—the standard deviation of test results obtained under reproducibility conditions.
R
3.1.19.1 Discussion—
Other measures of the dispersion of test results obtained under reproducibility conditions are the “reproducibility variance” and
the “reproducibility coefficient of variation.”
3.1.19.2 Discussion—
The reproducibility standard deviation includes, in addition to between-laboratory variability, the repeatability standard deviation
and a contribution from the interaction of laboratory factors (that is, differences between operators, equipment and environments)
with material factors (that is, the differences between properties of the materials other than that property of interest).
3.1.20 standard deviation, n—of a population, σ, the square root of the average or expected value of the squared deviation of a
variable from its mean; —of a sample,s, the square root of the sum of the squared deviations of the observed values in the sample
divided by the sample size minus 1. E2586
3.1.21 test determination, n—the value of a characteristic or dimension of a single test specimen derived from one or more
observed values. E2282
3.1.22 test method, n—a definitive procedure that produces a test result. E2282
3.1.23 test result, n—the value of a characteristic obtained by carrying out a specified test method. E2282
3.1.24 test specimen, n—the portion of a test unit needed to obtain a single test determination. E2282
3.1.25 test unit, n—the total quantity of material (containing one or more test specimens) needed to obtain a test result as specified
in the test method. See test result. E2282
3.1.26 trueness, n—the closeness of agreement between the population mean of the measurements or test results and the accepted
reference value.
3.1.26.1 Discussion—
“Population mean” is, conceptually, the average value of an indefinitely large number of test results
2 2
3.1.27 variance, σ , s , n— square of the standard deviation of the population or sample. E2586
4. 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.
E177 − 20
4.4 Accuracy—The term “accuracy,” used in earlier editions of Practice E177, embraces both precision and bias (see 9.3).
5. Test Method
5.1 Section 2 of the ASTM Regulations describes a test method as “a definitive procedure for the identification, measurement, and
evaluation of one or more qualities, characteristics, or properties of a material, product, system or service that produces a test
result.”
5.2 In this practice only quantitative test methods that produce numerical results are considered. Also, the word “material” is used
to mean material, product, system or service; the word “property” is used herein to mean that a quantitative test result can be
obtained that describes a characteristic or a quality, or some other aspect of the material; and “test method” refers to both the
document and the procedure described therein for obtaining a quantitative test result for one property. For a discussion of test
result, see 7.1.
5.3 A well-written test method specifies control over such factors as the test equipment, the test environment, the qualifications
of the operator (explicitly or implicitly), the preparation of test specimens, and the operating procedure for using the equipment
in the test environment to measure some property of the test specimens. The test method will also specify the number of test
specimens required and how measurements on them are to be combined to provide a test result (7.1), and might also reference a
sampling procedure appropriate for the intended use of the method.
5.4 It is necessary that the writers of the test method provide instructions or requirements for every known outside influence.
5.5 A test method conducted in a laboratory should demonstrate a long-term state of statistical control (see Refs. (1-3), Guide
E1488, and Practice E2587).
6. Measurement Terminology
6.1 A test result is the value obtained by carrying out the complete protocol of the test method once, being as simple as the result
of a single direct visual observation on a test specimen or the result of a complex series of automated procedures with the test result
calculation performed by a computer.
6.2 The following terms are used to describe partial results of the test method: observed value, and test determination, which are
more fully described in Guide E2282.
6.2.1 An observed value is interpreted as the most elemental single reading obtained in the process of making an observation. As
examples, an observation may involve a zero-adjusted micrometer reading of the thickness of a test strip at one position along the
strip or the weight of a subsample taken from a powder sample.
6.2.2 A test determination summarizes or combines one or more observed values. For example, (1) the measurement of the bulk
density of a powder may involve the observation of the mass and the tamped volume of the sample specimen, and the calculated
bulk density as the ratio mass/volume is a test determination; (2) the test determination of the thickness of a test specimen strip
may involve averaging micrometer caliper observations taken at several points along the strip.
6.2.3 A test result summarizes or combines one or more test determinations. For example, (1) a test method on bulk density might
require that the test determination of density for each of five subsamples of the powder sample be averaged to calculate the test
result; (2) a test method may involve multiple automated operations, combined with a calibration procedure, with many observed
values and test determinations, and the test result calculated and printed out by a computer.
6.3 Precision statements for ASTM test methods are applicable to comparisons between test results, not test determinations nor
observations, unless specifically and clearly indicated otherwise.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
E177 − 20
7. Sources of Variability
7.1 Sources of Variation of Test Results:
7.1.1 Generation of a test result involves an interpretation of the written document by an operator, who uses a specific unit and
version of the specified test apparatus, in the particular environment of this testing laboratory, to evaluate a specified number of
test specimens of the material to be tested. Replicate test results will differ due to changes in one or more of the above emphasized
experimental factors. Even when none of the experimental factors is intentionally changed, small changes usually occur. The
outcome of these changes may be seen as variability among the test results.
7.1.2 Each of the above experimental factors and all others, known and unknown, that can change the test result, are potential
sources of variability. Some of the more common factors are discussed in 7.2 – 7.6.
7.2 Operator:
7.2.1 Clarity of Test Method—Every effort must be made in preparing an ASTM standard test method to eliminate the possibility
of serious differences in interpretation. One way to check clarity is to observe, without comment, a competent laboratory operator,
not previously familiar with the method, apply the draft test method. If the operator has any difficulty, the draft most likely needs
revision.
7.2.2 Completeness of Test Method—It is necessary that operators, who are generally familiar with the test method or similar
methods, not read anything into the instructions that is not explicitly stated therein. Therefore, to ensure minimum variability due
to interpretation, procedural requirements must be complete.
7.2.2.1 If requirements are not explicitly stated in the test method (see 5.4), they must be included in the instructions for the
interlaboratory study (see Practice E691).
7.2.3 Differences in Operator Technique—Even when operators have been trained by the same instructor or supervisor to give
practically identical interpretations to the various steps of the test method, different operators (or even the same operator at different
times) may still differ in such things as dexterity, reaction time, color sensitivity, interpolation in scale reading, and so forth.
Unavoidable operator differences are thus one source of variability between test results. The test method should be designed and
described to minimize the effects of these operator sources of variability.
7.3 Apparatus:
7.3.1 Tolerances—In order to avoid prohibitive costs, only necessary and reasonable manufacturing and maintenance tolerances
can be specified. The variations allowed by these reasonable specification tolerances can be one source of variability between test
results from different sets of test equipment.
7.3.2 Calibration—One of the variables associated with the equipment is its state of calibration, including traceability to national
standards. The test method must provide guidance on the frequency of verification and of partial or complete recalibration; that
is, for each test determination, each test result, once a day, week, etc., or as required in specified situations. Calibration drift
introduces bias into test results over time. However, frequent unnecessary calibration contributes to variability of test results.
7.4 Environment:
7.4.1 The properties of many materials are sensitive to temperature, humidity, atmospheric pressure, atmospheric contaminants,
and other environmental factors. The test method usually specifies the standard environmental conditions for testing. However,
since these factors cannot be controlled perfectly within and between laboratories, a test method must be able to cope with a
reasonable amount of variability that inevitably occurs even though measurement and adjustment for the environmental variation
have been used to obtain control (see 5.5). Thus, the method must be robust to the differences between laboratories.
7.5 Sample (Test Specimens):
7.5.1 A lot (or shipment) of material must be sampled. Since it is unlikely that the material is perfectly uniform, sampling
variability is another source of variability among test results. In some applications, useful interpretation of test results may require
the measurement of the sampling error. In interlaboratory evaluation of test methods to determine testing variability, special
E177 − 20
attention is required in the selection of the material sample (see 10.3.4 and Practice E691) in order to obtain test specimens that
are as similar as possible. A small residual amount of material variability is almost always an inseparable component of any
estimate of testing variability.
7.5.2 Handling and size reduction of material during sampling can affect the test result when involving exposure to heat, light, and
the atmosphere. Testing of unstable materials requires attention to all aspects of the measurement operation, not just the test method
itself, to control both systematic error and variability.
7.6 Time:
7.6.1 Each of the above sources of variability (operator performance, equipment, environment, test specimens) may change with
time; for example, during a period when two or more test results are obtained. The longer the period, the less likely changes in
these sources will remain random (that is, the more likely systematic effects will enter), thereby increasing the net change and the
observed differences in test results. These differences will also depend on the degree of control exercised within the laboratory over
the sources of variability. In conducting an interlaboratory evaluation of a test method, the time span over which the measurements
are made should be kept as short as reasonably possible (see 8.2.4).
8. Precision
8.1 Precision:
8.1.1 The precision of a measurement process, and hence the stated precision of the test method from which the process is
generated, is a generic concept related to the closeness of agreement between test results obtained under prescribed conditions from
the measurement process being evaluated. The greater the dispersion or scatter of the test results, the poorer the precision. (It is
assumed that the resolution of the test apparatus is not so poor as to result in absolute agreement among observations and hence
among test results.) Measures of dispersion, usually used in statements about precision, are, in fact, direct measures of imprecision.
Although it may be stated quantitatively as the reciprocal of the standard deviation, precision is usually expressed as the standard
deviation or some multiple of the standard deviation (see 10.1).
8.1.2 The precision of the measurement process will depend on what sources (7.1 – 7.6) of variability are purposely included and
may also depend on the test level (see 10.3.4.1). An estimate of precision can be made and interpreted only if the experimental
situation (prescribed conditions) under which the test results are obtained is carefully described. There is no such thing as the
precision of a test method; a separate precision statement will apply to each combination of sources of variability.
8.1.3 Two conditions applicable to ASTM test methods are repeatability conditions and reproducibility conditions, and these lead
to estimates of the repeatability and reproducibility of a test method. Other conditions can be defined and are known collectively
as intermediate precision conditions. The long run variability within one laboratory is an intermediate precision condition of
particular importance (see 8.4.2).
8.2 Repeatability:
8.2.1 Repeatability is precision determined from multiple test results conducted under repeatability conditions, where the test
method is conducted by a single, well-trained operator using one set of equipment in a short period of time during which neither
the equipment nor the environment is likely to change appreciably. Any variability is due to small changes in conducting the test
operations and possible variation of the measured property among test samples. The latter is kept to a minimum by use of proper
sampling procedures in test sample preparation. All potential sources of variability must be carefully controlled within the
tolerances specified in the test method.
NOTE 1—If the test method requires a series of steps, the “single-operator-equipment” requirement means that for a particular step the same combination
of operator and equipment is used for every test result and on every material. Thus one operator may prepare th
...