ASTM C670-24a

Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials

ABSTRACT
This practice provides guidance in preparing precision and bias statements for ASTM test methods pertaining to construction materials. Test method shall conform to the maximum acceptable range of individual measurements. In order to be valid the indexes of precision to be included in the precision statement as guides for the operator must be based on estimates of the precision of the test method obtained from a statistically designed inter-laboratory series of tests. This series of tests must involve a sufficient number of laboratories, materials, and replicate measurements so that the results obtained provide reliable estimates of the true precision characteristic of the test method. The procedures described in this practice are based on the assumption that the proper estimates of precision have already been obtained. In any test method, tolerances are placed on the accuracy of measuring equipment. All tests made with a given set of equipment which has an error within the permitted tolerance will produce results with a small consistent bias, but that bias is not inherent in the test method and is not included in the bias statement for the test method. There are two conditions which permit the bias of a test method to be estimated: a standard reference sample of known value has been tested by the test method, and the test method has been applied to a sample which has been compounded in such a manner that the true value of the property being measured is known, such as may be the case, for example, in a test for cement content of concrete.
SCOPE
1.1 The Form and Style for ASTM Standards requires that all test methods contain statements on precision and bias. Further, the precision statement is required to contain a statement on single-operator precision (repeatability) and a statement on multilaboratory precision (reproducibility). This practice provides guidance for preparing precision and bias statements that comply with these requirements. Discussion of the purpose and significance of precision and bias statements for users of test methods is also provided. Examples of precision statements that conform to this practice are included in Appendix X1. This practice supplements Practice E177 and has been developed to meet the needs of ASTM Committees dealing with construction materials.  
Note 1: Although this practice is under the jurisdiction of Committee C09, the current version was developed jointly by Committees C01 and C09 and has subsequently been adopted for use by other committees dealing with construction materials.  
1.2 This practice assumes that an interlaboratory study (ILS) has been completed in accordance with Practice C802 or Practice E691. The interlaboratory study provides the necessary statistical values to write the precision and bias statements.  
1.3 The system of units for this practice is not specified. Dimensional quantities in the practice are presented only in examples of precision and bias statements.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the 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.

General Information

• Status: Published
• Publication Date: 31-Jan-2024
• ICS: 91.100.01 - Construction materials in general
• Technical Committee: C09 - Concrete and Concrete Aggregates
• Drafting Committee: C09.94 - Evaluation of Data (Joint C09 and C01)

Relations

• Replaces: ASTM C670-24 - Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• Effective Date: 01-Feb-2024
• Refers: ASTM E456-13a(2022) - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Referred By: ASTM D7175-23 - Standard Test Method for Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer
• Effective Date: 01-Feb-2024
• Referred By: ASTM C348-21 - Standard Test Method for Flexural Strength of Hydraulic-Cement Mortars
• Effective Date: 01-Feb-2024
• Referred By: ASTM C469/C469M-22 - Standard Test Method for Static Modulus of Elasticity and Poisson's Ratio of Concrete in Compression
• Effective Date: 01-Feb-2024
• Referred By: ASTM C302-13(2022) - Standard Test Method for Density and Dimensions of Preformed Pipe-Covering-Type Thermal Insulation
• Effective Date: 01-Feb-2024
• Referred By: ASTM C1567-23 - Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar Method)
• Effective Date: 01-Feb-2024
• Referred By: ASTM C1876-24 - Standard Test Method for Bulk Electrical Resistivity or Bulk Conductivity of Concrete
• Effective Date: 01-Feb-2024
• Referred By: ASTM C403/C403M-23 - Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance
• Effective Date: 01-Feb-2024
• Referred By: ASTM D994/D994M-11(2022) - Standard Specification for Preformed Expansion Joint Filler for Concrete (Bituminous Type)
• Effective Date: 01-Feb-2024
• Referred By: ASTM C1073-18(2023) - Standard Test Method for Hydraulic Activity of Slag Cement by Reaction with Alkali
• Effective Date: 01-Feb-2024
• Referred By: ASTM C1170/C1170M-20 - Standard Test Method for Determining Consistency and Density of Roller-Compacted Concrete Using a Vibrating Table
• Effective Date: 01-Feb-2024
• Referred By: ASTM C928/C928M-20a - Standard Specification for Packaged, Dry, Rapid-Hardening Cementitious Materials for Concrete Repairs
• Effective Date: 01-Feb-2024
• Referred By: ASTM D6927-22 - Standard Test Method for Marshall Stability and Flow of Asphalt Mixtures
• Effective Date: 01-Feb-2024

Overview

ASTM C670-24a, titled Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials, provides a structured approach for drafting precision and bias statements in ASTM test methods related to construction materials. The practice is essential for ensuring that test methods reliably reflect the true variability and performance of materials by incorporating comprehensive statistical analysis from interlaboratory studies.

This standard supports consistency and transparency in reporting the expected precision and bias associated with test results, enabling both laboratories and end users to interpret testing outcomes with confidence. ASTM C670-24a is recognized under international standardization principles and is referenced by regulatory agencies and industry stakeholders concerned with the quality assurance of construction materials testing.

Key Topics

• Precision and Bias Definitions: Clarifies terms such as single-operator precision (repeatability), multilaboratory precision (reproducibility), and bias for construction materials test methods.
• Statistical Foundations: Guidance is based on data derived from statistically designed interlaboratory studies as specified in related ASTM practices (such as ASTM C802 and ASTM E691).
• Types of Precision:
  • Single-operator precision: Variability when the same operator uses the same apparatus in one lab.
  • Multilaboratory precision: Variability across different labs, operators, and equipment.
  • Acceptable range: Defines allowable differences between multiple test results or determinations.
• Preparation of Statements: Outlines how statements should be drafted, including required statistical values, summary information about the study, and structure for reporting both precision and bias.
• Bias Statement Development: Provides criteria for when and how bias statements can be developed, based on the availability of reference materials or known values.
• Temporary Statements: Allows interim single-operator precision statements when full interlaboratory data is yet to be compiled.

Applications

ASTM C670-24a is widely applied in:

• Developing and Revising Test Methods: Ensuring all ASTM test methods for construction materials include clear and compliant statements on precision and bias.
• Quality Control and Specification Setting: Supporting the calculation of specification limits by accounting for test method variability, helping both producers and consumers make informed decisions about material acceptability.
• Operator Qualification: Providing performance metrics for training, qualifying, and auditing laboratory personnel based on repeatability standards.
• Comparison and Harmonization: Facilitating the comparison of test results between laboratories, especially in international contexts where methods harmonization and regulatory compliance are essential.
• Research and Data Reporting: Mandating rigorous reporting requirements that support transparency and reproducibility in materials science research.

Related Standards

For comprehensive implementation, ASTM C670-24a should be used in conjunction with several related ASTM standards and terminology:

• ASTM C802: Practice for Conducting an Interlaboratory Test Program for Construction Materials.
• ASTM E177: Practice for Use of the Terms Precision and Bias in ASTM Test Methods.
• 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 C1067: Practice for Conducting a Ruggedness Evaluation or Screening Program.
• ASTM D6607: Practice for Inclusion of Precision Statement Variation in Specification Limits.

Practical Value

Implementing ASTM C670-24a ensures the reliability, repeatability, and transparency of laboratory testing for construction materials. The practice is crucial for:

• Enhancing confidence in test data across the construction industry.
• Meeting regulatory and quality assurance requirements.
• Improving the credibility of standards-compliant laboratories.
• Facilitating international trade and acceptance of materials by adhering to recognized standardization principles.

Keywords: ASTM C670-24a, precision and bias statements, construction materials testing, test method reliability, laboratory reproducibility, quality assurance, interlaboratory study, test specification limits.

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: C670 − 24a
Standard Practice for
Preparing Precision and Bias Statements for Test Methods
for Construction Materials
This standard is issued under the fixed designation C670; 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* Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.1 The Form and Style for ASTM Standards requires that
Barriers to Trade (TBT) Committee.
all test methods contain statements on precision and bias.
Further, the precision statement is required to contain a
2. Referenced Documents
statement on single-operator precision (repeatability) and a
statement on multilaboratory precision (reproducibility). This
2.1 ASTM Standards:
practice provides guidance for preparing precision and bias C802 Practice for Conducting an Interlaboratory Test Pro-
statements that comply with these requirements. Discussion of
gram to Determine the Precision of Test Methods for
the purpose and significance of precision and bias statements Construction Materials
for users of test methods is also provided. Examples of
C1067 Practice for Conducting a Ruggedness Evaluation or
precision statements that conform to this practice are included Screening Program for Test Methods for Construction
in Appendix X1. This practice supplements Practice E177 and Materials
has been developed to meet the needs of ASTM Committees D6607 Practice for Inclusion of Precision Statement Varia-
dealing with construction materials. tion in Specification Limits
E177 Practice for Use of the Terms Precision and Bias in
NOTE 1—Although this practice is under the jurisdiction of Committee
ASTM Test Methods
C09, the current version was developed jointly by Committees C01 and
E456 Terminology Relating to Quality and Statistics
C09 and has subsequently been adopted for use by other committees
dealing with construction materials.
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.2 This practice assumes that an interlaboratory study
(ILS) has been completed in accordance with Practice C802 or
3. Terminology
Practice E691. The interlaboratory study provides the neces-
sary statistical values to write the precision and bias state-
3.1 Definitions:
ments.
3.1.1 For definitions of general statistical terms, refer to
Terminology E456.
1.3 The system of units for this practice is not specified.
Dimensional quantities in the practice are presented only in
3.2 Definitions of Terms Specific to This Standard:
examples of precision and bias statements.
3.2.1 test determination, n—the value of a characteristic of
1.4 This standard does not purport to address all of the a single test specimen obtained by a specified test method.
safety concerns, if any, associated with its use. It is the
3.2.1.1 Discussion—The term “replicate” is often used for
responsibility of the user of this standard to establish appro-
each test determination if multiple determinations are required
priate safety, health, and environmental practices and deter-
to obtain a test result (see 4.1).
mine the applicability of regulatory limitations prior to use.
3.2.2 test result, n—the value of a characteristic of a
1.5 This international standard was developed in accor-
material obtained by carrying out a specified test method.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the 3.2.2.1 Discussion—A test result may be a single test
This practice is under the jurisdiction of ASTM Committee C09 on Concrete
and Concrete Aggregates and is the direct responsibility of Subcommittee C09.94 For referenced ASTM standards, visit the ASTM website, www.astm.org, or
on Evaluation of Data (Joint C09 and C01). contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved Feb. 1, 2024. Published March 2024. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 1971. Last previous edition approved in 2024 as C670 – 24. DOI: the ASTM website.
10.1520/C0670-24A. Terms are listed in order of hierarchy beginning with the basic concept.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C670 − 24a
determination or the average of a specified number of test apparatus have been used in different laboratories for which the
determinations, or replicates (see 4.1). environments may have differed. These factors may lead to a
between-laboratory component of variance that is determined
3.2.3 identical test specimens, n—test specimens selected at
random and made from a single quantity or batch of material from the interlaboratory study and contributes to the multilabo-
ratory variance. In Practice E177, the multilaboratory standard
that is as homogeneous as possible.
deviation is referred to as the reproducibility standard devia-
3.2.3.1 Discussion—In interlaboratory studies of test meth-
tion and the subscript R is used.
ods for fresh cementitious mixtures, a practicable approach for
3.2.6 difference limit (d2s or d2s%), n—the difference be-
obtaining identical tests specimens is to assemble technicians
tween two test results that is expected to be exceeded with a
from different laboratories at one location and test specimens
probability of about 5 % in the normal and correct operation of
are made from the same batch of the fresh mixture. For
the test method; used as an index of precision of the test
interlaboratory studies of nondestructive test methods, the
method.
same test specimens can be circulated among participating
3.2.6.1 Discussion—The difference limit has been selected
laboratories, provided the characteristic of interest does not
as the appropriate index of precision in most precision state-
change during the time to complete the study.
ments. A difference limit (d2s) indicates the maximum accept-
3.2.4 single-operator standard deviation, s , (or coeffıcient
r
able difference between two test results obtained on identical
of variation, CV ), n—the standard deviation (or coefficient of
r
test specimens (see 3.2.3.1) under the applicable system of
variation) of test determinations obtained on identical test
causes (single-operator or multilaboratory conditions). The
specimens by a single operator using the same apparatus in the
(d2s%) limit is the maximum acceptable difference between
same laboratory over a relatively short period of time.
two test results expressed as a percentage of their average.
3.2.4.1 Discussion—The single-operator standard deviation,
These difference limits are calculated by multiplying the
or coefficient of variation, is the fundamental statistic under-
appropriate standard deviation (s or s ) or coefficient of
r R
lying the single-operator indexes of precision. The single-
variation (CV or CV ) by the factor 1.96 =2, which for the
r R
operator standard deviation, or coefficient of variation, is an
purpose of this Practice is taken to be equal to 2.8. In Practice
indication of the variability of a large number of test determi-
E177, the terms repeatability limit and reproducibility limit are
nations by the same operator on the same material. This value
used for these difference limits under single-operator and
is obtained from an interlaboratory study and is equal to the
multilaboratory conditions, respectively.
pooled standard deviation of test determinations obtained by
3.2.7 acceptable range, n—the difference between the larg-
the operators. The coefficient of variation (ratio of standard
est and smallest of three or more test determinations or test
deviation to the average expressed as a percentage) is used if
results that is expected to be exceeded with a probability of
the standard deviation is proportional to the level of the
about 5 % in the normal and correct operation of the test
characteristic being measured. The single-operator standard
method; used as an index of precision of the test method, if
deviation, usually considered a property of the test method,
applicable.
will generally be lower than the multilaboratory standard
deviation. In Practice E177, the single-operator standard de-
3.2.7.1 Discussion—This index is usually reported in preci-
viation is referred to as the repeatability standard deviation,
sion statements of test methods that define a test result as the
and the subscript r is used. In previous versions of Practice
average of three or more determinations. Otherwise, the
C670, the terms one-sigma limit (1s) or one sigma limit in
difference limit (d2s or d2s%) is used. See 4.3 for additional
percent (1s%) were used for the single-operator standard
discussion on how to determine this index.
deviation or single-operator coefficient of variation, respec-
tively. In some publications, the term within-test standard
4. General Concepts
deviation (or coeffıcient of variation) has been used. The term
4.1 Test Result—The result of a test method may be a single
within-laboratory standard deviation (or coefficient of varia-
test determination or the average of two or more test determi-
tion) should not be used for this statistic (see 4.2.3).
nations (or replicates). The precision statement of a test method
3.2.5 multilaboratory standard deviation, s (or coeffıcient
R
applies to a test result as defined in the test method and the
of variation, CV ), n—the standard deviation or coefficient of
R
statement should indicate what constitutes a test result.
variation of test results obtained with the same test method on
4.1.1 Number of Test Determinations—The number of test
identical test specimens in different laboratories with different
determinations required to obtain a test result by a test method
operators using different equipment.
must be taken into account when evaluating testing variations.
3.2.5.1 Discussion—The multilaboratory standard The statistic used in evaluating single-operator precision is
deviation, or coefficient of variation, is the fundamental statis- based on the standard deviation (or coefficient of variation) of
tic underlying the indexes of precision under multilaboratory single test determinations.
conditions. The multilaboratory standard deviation is an indi- 4.1.2 Test Result Based on Averages of Determinations—
cation of the variability of test results obtained by different For test methods that define a test result as the average of two
laboratories for identical test specimens. The multilaboratory or more test determinations (or replicates), the fundamental
standard deviation (or coefficient of variation) is usually statistic is still the standard deviation (or coefficient of varia-
greater than the single-operator standard deviation (or coeffi- tion) of single test determinations. The report of the analysis of
cient of variation), because different operators and different the interlaboratory study (see 5.2) must include this statistic.
C670 − 24a
suspected of producing erratic results, and a closer examination of the
The single-operator standard deviation of test determinations
procedures would be in order. If knowledge about the test method in
can be used to calculate the standard deviation of a test result
question indicates that certain actions may be appropriate in cases where
that is the average of multiple determinations and thereby
inconsistent results occur, then such information should be included in the
define the maximum acceptable difference between two test
test method, but details of how this should be done will depend upon the
results obtained by the same operator on identical test speci-
particular test method.
mens. The precision statement may also include the maximum
4.2.2 Multilaboratory Precision—The multilaboratory stan-
acceptable range of individual determinations that comprise the
dard deviation (or coefficient of variation) obtained from the
test result (see 4.3).
interlaboratory study provides a measure of the greatest differ-
4.1.3 Standard Deviation of an Average—The standard
ence between two test determinations that would be considered
deviation of the average of n test determinations obtained from
acceptable when properly conducted tests are made by two
identical specimens taken from the same population is equal to
different operators in different laboratories on identical test
the standard deviation of the individual determinations divided
specimens. If results differ by more than the difference limit
by the square root of n. This relationship is valid, however,
(d2s) or (d2s%), there is a high probability that one or both
only if the determinations are obtained using identical speci-
laboratories are in error or that a difference exists in the
mens. It is not applicable to averages obtained on specimens
characteristics of the test specimens used for the tests. In such
made from different batches of cementitious mixtures as
cases, retests should be made. If possible, newly drawn test
discussed in 4.2.3.
specimens should be used for such retests.
4.2 Types of Precision—A precision statement meeting the
4.2.2.1 If the test method calls for reporting the average of
requirements of this practice normally contains two main
more than one test determination, multilaboratory precision is
elements: (1) single-operator precision, and (2) multilaboratory
expressed as a maximum allowable difference between aver-
precision. For test methods that require test results on speci-
ages of such groups obtained by two laboratories (Note 3). In
mens made from more than one batch, the single-operator,
this case, the multilaboratory standard deviation derived from
multi-batch precision is also included.
the interlaboratory study is based on the number of replications
4.2.1 Single-Operator Precision—The pooled, single-
required to obtain a test result as defined by the test method.
operator standard deviation (or coefficient of variation) of test
determinations obtained from the interlaboratory study is the
NOTE 3—Example 5 in Appendix X1 shows an example of this
fundamental statistic of the test method. This is used to
situation. If a test result is based on tests of specimens made from different
calculate the greatest difference between two or more determi-
batches of the cementitious mixture, the consideration in 4.2.3 apply, and
nations that would be considered acceptable when properly
Example 6 provides an example of this situation.
conducted repetitive determinations are made on the same
4.2.3 Single-Operator, Multi-Batch Precision—Some test
material by a competent operator. As discussed in 4.1.2, the
methods require reporting the averages of two or more deter-
single-operator standard deviation (or coefficient of variation)
minations obtained on specimens from two or more batches
of test determinations is also used to calculate the greatest
made using the same materials. The single-operator, multi-
acceptable difference between test results defined as the aver-
batch standard deviation is a measure of the variation of the
age of two or more determinations. The single-operator preci-
averages among the batches. This standard deviation will
sion provides a quantitative guide to acceptable performance
usually be greater than the value obtained by dividing the
by an operator. If two determinations or test results by the same
single-operator standard deviation by the square root of the
operator differ by more than the difference limit, (d2s) or
number of determinations used to obtain the average test result
(d2s%), or if the range of more than two determinations or test
for each batch. This is because the single-operator, multi-batch
results exceeds the values defined in 4.3, there is a high
standard deviation includes the batch-to-batch variability. The
probability that an error has occurred and retests should be
precision statement for this type of test method will include
made.
three indexes of precision: (1) the single-operator precision, (2)
NOTE 2—It is beyond the scope of this practice to describe in detail
the single-operator, multi-batch precision, and (3) the multi-
what action should be taken in all cases if two test results differ by more
laboratory precision. In some test methods, the term within-
than the (d2s) or (d2s%) limits or the range of more than two determina-
laboratory precision has been used. The preferred term,
tions exceeds the maximum expected range. Such an occurrence is a
warning that there may have been some error in the test procedure, or
however, is single-operator, multi-batch precision because this
some departure from the prescribed conditions of the test on which the
is more descriptive of the conditions under which results are
limits stated in the test method are based; for example, there may have
obtained. The single-operator, multi-batch precision statement
been faulty or misadjusted apparatus or improper environmental condi-
would indicate the acceptable range (or difference limit, if only
tions in the laboratory. In judging whether results are in error, information
other than the difference between two test results is needed. Often a review
two batches are involved) among batch averages. The advice of
of the circumstances under which the test results in question were obtained
a statistical consultant should be sought in planning the
will reveal some reason for inconsistent results. In this case, the data
interlaboratory study for this type of test method so that the
should be discarded and new test results obtained and evaluated sepa-
necessary statistics can be determined.
rately. If no physical reason for inconsistent results is found, retests should
still be made, but the original tests should not be ignored. If the second set
4.2.4 Other Measures of Precision—The elements described
of results also differs by more than the applicable limit, the evidence is
in 4.2.1, 4.2.2, and 4.2.3 involve the main systems of causes of
strong that something is wrong or that a real difference exists between the
variability in test results that are of interest to users of test
specimens tested. If the second set produces a result within the limit, it
may be taken as a valid test, but the operator or laboratory may then be methods involving construction materials. In cases where other
C670 − 24a
systems of causes apply (for example, single-operator- inherent variability of the test method along with the material
apparatus, multi-day precision; or multi-operator, single-day- variability. The variability associated with the test method may
apparatus precision), the appropriate statistics for those sys- be reduced by requiring a test result to be the average of two
tems of causes need to be developed and the appropriate or more test determinations. A balance, however, needs to be
combination of modifiers given in Practice E177 should be achieved between the incremental cost of additional testing and
used to describe those statistics. These should not, however, be the corresponding incremental reduction in uncertainty. Also,
taken as the fundamental precision parameters for the test increasing the number of determinations to obtain a test result
method. The advice of a statistical consultant should be sought may have a minor effect on multilaboratory variability if the
in planning the interlaboratory study so that the correct between-laboratory component of variance is greater than the
statistics can be determined. single-operator variance. Because specification limits should
be established with consideration of testing variability and
4.3 Acceptable Range Among Results—If the test method
material variability, it is not appropriate to consider the indexes
requires more than two test results, as so defined in the method,
of precision of the test method as tolerances to be added to
the difference between highest and lowest test results in the
statistically-derived specification limits for the purpose of
group must be compared to the maximum acceptable range for
judging acceptance or rejection of materials.
the applicable system of causes. The range among different
4.4.2 For Qualifying an Operator—As discussed in 4.2.1,
numbers of test results in the group, including two, that would
indexes of single-operator precision are sometimes used as a
be expected to be exceeded with no more than about 5 %
basis for qualifying an operator. The assumption is that results
probability is obtained by multiplying the appropriate standard
that do not differ by more than the stated index are indicative
deviation or coefficient of variation by the corresponding factor
of proper performance of the test. This assumption, however, is
from the second column of Table 1. If more than two test
not necessarily correct. Uniform misunderstanding of
results are obtained, the index of precision for the difference
instructions, incorrect specimen preparation, or maladjust-
between two results cannot be used as a criterion for judging
ments of equipment may produce consistent but erroneous test
acceptability of the differences between pairs of results se-
results. Whenever possible, tests conducted for the purpose of
lected from the group.
qualifying an operator should be made on materials for which
4.4 Uses of Indexes of Precision
the measured characteristic is known, so that bias as well as
4.4.1 In Setting Specification Limits—The indexes of preci-
precision can be evaluated. Participation in proficiency sample
sion described in this practice are applicable to test results
programs is an effective way to evaluate operator performance
obtained on identical test specimens and provide information
among peers.
on the inherent variability of the test method. In routine quality
5. Basis for Precision Statement
control or acceptance testing for a project, the variation of the
test results will be affected by the inherent variability of the test
5.1 In order to be valid, the indexes of precision to be
method, the variability of the materials, and the variability
included in the precision statement must be based on estimates
associated with the sampling method. Specifiers need to
of the precision of the test method obtained from a statistically
consider these sources of variability in setting specification
designed interlaboratory study. Before proceeding with the
limits so as to control the producer’s risk of rejection of a lot
interlaboratory study, the ruggedness of the test method should
of acceptable material and the purchaser’s risk of accepting a
be investigated in accordance with Practice C1067. A rugged-
lot of deficient material. Practice D6607 provides a method-
ness evaluation involves the participation of a few laboratories
ology for setting specification limits that accounts for the
and the use of several materials that encompass the range of the
level of the characteristics to be measured by the test method.
This evaluation will provide a preliminary estimate of single-
Philleo, R. E., “Establishing Specification Limits for Materials,” Cement,
operator precision and may indicate whether tighter tolerances
Concrete, and Aggregates, CCAGDP, Vol. 1, No. 2, 1979, pp. 83-87.
are needed for key aspects of the test method. The interlabo-
ratory study, on the other hand, must involve a sufficient
A
TABLE 1 Maximum Acceptable Range of Test Results
number of laboratories, materials, and replicate measurements
Multiplier of Standard
so that the results obtained provide reliable estimates of the
Number of
Deviation or Coefficient
Test Results
B
precision of the test method (Note 4). The procedures described
of Variation
in this practice assume that proper estimates of precision have
2 2.8
3 3.3
been obtained. Practice C802 is a companion document that
4 3.6
describes how to organize and conduct a suitable interlabora-
5 3.9
tory study and how to analyze the data to obtain the relevant
6 4.0
7 4.2
estimates of precision.
8 4.3
9 4.4 NOTE 4—The requirement of “reliable estimates of the precision”
10 4.5
presupposes an estimate obtained from a properly designed and executed
A interlaboratory series of tests involving at least 30 degrees of freedom for
A test result can be a single determination or the average of two or more
single-operator standard deviation and at least 10 laboratories. See
determinations as defined in the test method.
B
Practice C802.
Values were obtained from Table A7 of “Order Statistics and Their Use in Testing
and Estimation,” Vol 1, by Leon Harter, Aerospace Research Laboratories, United
5.2 The Form and Style for ASTM Standards requires that
States Air Force.
data and details of the interlaboratory study used to determine
C670 − 24a
precision and bias be filed as a research report at ASTM characteristics measured, and number of test determinations
International Headquarters. (replicate tests) for each material. The research report (see 5.2)
should be referenced for the details of the interlaboratory study
5.3 The ASTM International Interlaboratory Study Program
and the data analysis leading to the precision statement. This
(ILS) can support subcommittees in the development of
summary information should be provided in a note.
precision statements by assisting in the design of an interlabo-
ratory study, distribution of materials or test specimens, data
NOTE 5—Example 1 in Appendix X1 illustrates the wording that may
be used in a note to summarize the interlaboratory study. The subcom-
analysis, and preparation of a draft research report.
mittee should exercise its discretion in choosing the exact wording for the
5.4 A subcommittee may wish to postpone the organization
note as this will depend on the nature of the test method and the actual
of the interlaboratory study until a new test method has been
interlaboratory study.
approved. In such cases, the precision statement of the new test
6.1.2 Information on Units—Many precision indexes for
method must include the single-operator standard-deviation (or
test methods of construction materials are based on data
coefficient of variation) obtained in at least one laboratory.
obtained using the inch-pound version of a combined standard
Preferably, the standard deviation (or coefficient of variation)
and these indexes have been converted to SI units. The
should be obtained by using materials with different levels of
following examples provide recommended wording for a note
the characteristic being measured. A ruggedness evaluation in
to the precision statement, if applicable, and how the conver-
accordance with Practice C1067 can be a source of data to
sion should be performed.
develop a temporary precision statement. The temporary state-
6.1.2.1 Case 1—Pr
...

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: C670 − 24 C670 − 24a
Standard Practice for
Preparing Precision and Bias Statements for Test Methods
for Construction Materials
This standard is issued under the fixed designation C670; 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 Form and Style for ASTM Standards requires that all test methods contain statements on precision and bias. Further, the
precision statement is required to contain a statement on single-operator precision (repeatability) and a statement on
multilaboratory precision (reproducibility). This practice provides guidance for preparing precision and bias statements that
comply with these requirements. Discussion of the purpose and significance of precision and bias statements for users of test
methods is also provided. Examples of precision statements that conform to this practice are included in Appendix X1. This
practice supplements Practice E177 and has been developed to meet the needs of ASTM Committees dealing with construction
materials.
NOTE 1—Although this practice is under the jurisdiction of Committee C09, the current version was developed jointly by Committees C01 and C09 and
has subsequently been adopted for use by other committees dealing with construction materials.
1.2 This practice assumes that an interlaboratory study (ILS) has been completed in accordance with Practice C802 or Practice
E691. The interlaboratory study provides the necessary statistical values to write the precision and bias statements.
1.3 The system of units for this practice is not specified. Dimensional quantities in the practice are presented only in examples
of precision and bias statements.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the 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.
2. Referenced Documents
2.1 ASTM Standards:
C802 Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Methods for Construction
Materials
This practice is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee C09.94 on
Evaluation of Data (Joint C09 and C01).
Current edition approved Jan. 1, 2024Feb. 1, 2024. Published March 2024. Originally approved in 1971. Last previous edition approved in 20152024 as
C670 – 15.C670 – 24. DOI: 10.1520/C0670-24.10.1520/C0670-24A.
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’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C670 − 24a
C1067 Practice for Conducting a Ruggedness Evaluation or Screening Program for Test Methods for Construction Materials
D6607 Practice for Inclusion of Precision Statement Variation in Specification Limits
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions:
3.1.1 For definitions of general statistical terms, refer to Terminology E456.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 test determination, n—the value of a characteristic of a single test specimen obtained by a specified test method.
3.2.1.1 Discussion—
The term “replicate” is often used for a test determination.each test determination if multiple determinations are required to obtain
a test result (see 4.1).
3.2.2 test result, n—the value of a characteristic of a material obtained by carrying out a specified test method.
3.2.2.1 Discussion—
A test result may be a single test determination or the average of a specified number of test determinations, or replicates (see 4.1
for additional discussion). ).
3.2.3 identical test specimens, n—test specimens selected at random and made from a single quantity or batch of material that is
as homogeneous as possible.
3.2.3.1 Discussion—
In interlaboratory studies of test methods for fresh cementitious mixtures, a practicable approach for obtaining identical tests
specimens is to assemble technicians from different laboratories at one location and test specimens are made from the same batch
of the fresh mixture. For interlaboratory studies of nondestructive test methods, the same test specimens can be circulated among
participating laboratories, provided the characteristic of interest does not change during the time to complete the study.
3.2.4 single-operator standard deviation, s , (or coeffıcient of variation, CV ), n—the standard deviation (or coefficient of
r r
variation) of test determinations obtained on identical test specimens by a single operator using the same apparatus in the same
laboratory over a relatively short period of time.
3.2.4.1 Discussion—
The single-operator standard deviation, or coefficient of variation, is the fundamental statistic underlying the single-operator
indexes of precision. The single-operator standard deviation, or coefficient of variation, is an indication of the variability of a large
groupnumber of test determinations by the same operator on the same material. This value is obtained from an interlaboratory study
and is equal to the pooled standard deviation of test determinations obtained by the operators. The coefficient of variation (ratio
of standard deviation to the average expressed as a percentage) is used if the standard deviation is proportional to the level of the
characteristic being measured. The single-operator standard deviation, usually considered a property of the test method, will
generally be lower than the multilaboratory standard deviation. In Practice E177, the single-operator standard deviation is referred
to as the repeatability standard deviation, and the subscript r is used. In previous versions of Practice C670, the terms one-sigma
limit (1s) or one sigma limit in percent (1s%) were used for the single-operator standard deviation or single-operator coefficient
of variation, respectively. In some publications, the term within-test standard deviation (or coeffıcient of variation) has been used.
The term within-laboratory standard deviation (or coefficient of variation) should not be used for this statistic (see 4.2.3).
3.2.5 multilaboratory standard deviation, s (or coeffıcient of variation, CV ), n—the standard deviation or coefficient of variation
R R
of test results obtained with the same test method on identical test specimens in different laboratories with different operators using
different equipment.
3.2.5.1 Discussion—
The multilaboratory standard deviation, or coefficient of variation, is the fundamental statistic underlying the indexes of precision
under multilaboratory conditions. The multilaboratory standard deviation is an indication of the variability of a group of test results
Terms are listed in order of hierarchy beginning with the basic concept.
C670 − 24a
obtained by different laboratories for identical test specimens. The multilaboratory standard deviation (or coefficient of variation)
is usually greater than the single-operator standard deviation (or coefficient of variation), because different operators and different
apparatus have been used in different laboratories for which the environments may have differed. These factors may lead to a
between-laboratory component of variance that is determined from the interlaboratory study and contributes to the multilaboratory
variance. In Practice E177, the multilaboratory standard deviation is referred to as the reproducibility standard deviation and the
subscript R is used.
3.2.6 difference limit (d2s or d2s%), n—the difference between two test results that is expected to be exceeded with a probability
of about 5 % in the normal and correct operation of the test method; used as an index of precision of the test method.
3.2.6.1 Discussion—
The difference limit has been selected as the appropriate index of precision in most precision statements. A difference limit (d2s)
indicates the maximum acceptable difference between two test results obtained on identical test specimens (see 3.2.3.1) under the
applicable system of causes (single-operator or multilaboratory conditions). The (d2s%) limit is the maximum acceptable
difference between two test results expressed as a percentage of their average. These difference limits are calculated by multiplying
=
the appropriate standard deviation (s or s ) or coefficient of variation (CV or CV ) by the factor 1.96 2, which for the purpose
r R r R
of this Practice is taken to be equal to 2.8. In Practice E177, the terms repeatability limit and reproducibility limit are used for these
difference limits under single-operator and multilaboratory conditions, respectively.
3.2.7 acceptable range, n—the difference between the largest and smallest of three or more test determinations or test results that
is expected to be exceeded with a probability of about 5 % in the normal and correct operation of the test method; used as an index
of precision of the test method, if applicable.
3.2.7.1 Discussion—
This index is usually reported in precision statements of test methods that define a test result as the average of three or more
determinations. Otherwise, the difference limit (d2s or d2s%) is used. See 4.3 for additional discussion on how to determine this
index.
4. General Concepts
4.1 Test Result—The result of a test method may be a single test determination or the average of two or more test determinations
(or replicates). The precision statement of a test method applies to a test result as defined in the test method and should state clearly
this fact. the statement should indicate what constitutes a test result.
4.1.1 Number of Test Determinations—The number of test determinations required to obtain a test result by a test method must
be taken into account when evaluating testing variations. The statistic used in evaluating single-operator precision is based usually
on the standard deviation (or coefficient of variation) of single test determinations. The single-operator standard deviation (or
coefficient of variation) may be used in evaluating the acceptable range of test determinations.
4.1.2 Test Result Based on Averages of Determinations—For test methods that define a test result as the average of two or more
test determinations (or replicates), the fundamental statistic is still the standard deviation (or coefficient of variation) of single test
determinations. The report of the analysis of the interlaboratory study (see 5.2) must include this statistic. The single-operator
standard deviation of test determinations can be used to calculate the standard deviation of a test result that is the average of
multiple determinations and thereby define the maximum acceptable difference between two test results obtained by the same
operator on identical test specimens. The precision statement may also include the maximum acceptable range of individual
determinations that comprise the test result (see 4.3).
4.1.3 Standard Deviation of an Average—The standard deviation of the average of n test determinations obtained from identical
specimens taken from the same population is equal to the standard deviation of the individual determinations divided by the square
root of n. This relationship is valid, however, only if the determinations are obtained using identical specimens. It is not applicable
to averages obtained on specimens made from different batches of cementitious mixtures as discussed in 4.2.3.
4.2 Types of Precision—A precision statement meeting the requirements of this practice normally contains two main elements: (1)
single-operator precision, and (2) multilaboratory precision. For test methods that require test results on specimens made from
more than one batch, the single-operator, multi-batch precision is also included.
4.2.1 Single-Operator Precision—The pooled, single-operator standard deviation (or coefficient of variation) of test determina-
tions obtained from the interlaboratory study is the underlyingfundamental statistic of the test method. This is used to calculate
the greatest difference between two or more determinations that would be considered acceptable when properly conducted
C670 − 24a
repetitive determinations are made on the same material by a competent operator. As discussed in 4.1.2, the single-operator
standard deviation (or coefficient of variation) of test determinations is also used to calculate the greatest acceptable difference
between test results defined as the average of two or more determinations. The single-operator precision provides a quantitative
guide to acceptable performance by an operator. If two determinations or test results by the same operator differ by more than the
difference limit, (d2s) or (d2s%), or if the range of more than two determinations or test results exceeds the values defined in 4.3,
there is a high probability that an error has occurred and retests should be made.
NOTE 2—It is beyond the scope of this practice to describe in detail what action should be taken in all cases if two test results differ by more than the
(d2s) or (d2s%) limits or the range of more than two determinations exceeds the maximum expected range. Such an occurrence is a warning that there
may have been some error in the test procedure, or some departure from the prescribed conditions of the test on which the limits appearingstated in the
test method are based; for example, there may have been faulty or misadjusted apparatus or improper environmental conditions in the laboratory. In
judging whether or not results are in error, information other than the difference between two test results is needed. Often a review of the circumstances
under which the test results in question were obtained will reveal some reason for a departure.inconsistent results. In this case, the data should be discarded
and new test results obtained and evaluated separately. If no physical reason for a departureinconsistent results is found, retests should still be made, but
the original tests should not be ignored. If the second set of results also differs by more than the applicable limit, the evidence is very strong that something
is wrong or that a real difference exists between the specimens tested. If the second set produces a result within the limit, it may be taken as a valid test,
but the operator or laboratory may then be suspected of producing erratic results, and a closer examination of the procedures would be in order. If
knowledge about the test method in question indicates that certain actions may be appropriate in cases where deviantinconsistent results occur, then such
information should be included in the test method, but details of how this should be done will depend upon the particular test method.
4.2.2 Multilaboratory Precision—The multilaboratory standard deviation (or coefficient of variation) obtained from the
interlaboratory study provides a measure of the greatest difference between two test determinations that would be considered
acceptable when properly conducted tests are made by two different operators in different laboratories on portions of a material
that are intended to be identical, or as nearly identical as possible.identical test specimens. If results differ by more than the
difference limit (d2s) or (d2s%), there is a high probability that one or both laboratories are in error or that a difference exists in
the characteristics of the test specimens used for the tests. In such cases, retests should be made. If possible, newly drawn test
specimens should be used for such retests.
4.2.2.1 If the test method calls for reporting the average of more than one test determination, multilaboratory precision is
expressed as a maximum allowable difference between averages of such groups obtained by two laboratories (Note 3). In this case,
the multilaboratory standard deviation derived from the interlaboratory study is based on the number of replications required to
obtain a test result as defined by the test method.
NOTE 3—Example 5 in Appendix X1 shows an example of this situation. If a test result is based on tests of specimens made from different batches of
the cementitious mixture, the consideration in 4.2.3 apply, and Example 6 provides an example of this situation.
4.2.3 Single-Operator, Multi-Batch Precision—Some test methods require reporting the averages of two or more determinations
obtained on specimens from two or more batches made using the same materials. The single-operator, multi-batch standard
deviation is a measure of the variation of the averages among the batches. This standard deviation will usually be greater than the
value obtained by dividing the single-operator standard deviation by the square root of the number of determinations used to obtain
the average test result for each batch. This is because the single-operator, multi-batch standard deviation includes the
batch-to-batch variability. The precision statement for this type of test method will include three indexes of precision: (1) the
single-operator precision, (2) the single-operator, multi-batch precision, and (3) the multilaboratory precision. In some test
methods, the term within-laboratory precision has been used. The preferred term, however, is single-operator, multi-batch
precision because this is more descriptive of the conditions under which results are obtained. The single-operator, multi-batch
precision statement would indicate the acceptable range (or difference limit, if only two batches are involved) among batch
averages. The advice of a statistical consultant should be sought in planning the interlaboratory study for this type of test method
so that the necessary statistics can be determined.
4.2.4 Other Measures of Precision—The elements described in 4.2.1, 4.2.2, and 4.2.3 involve the main systems of causes of
variability in test results that are of interest to users of test methods involving construction materials. In cases where other systems
of causes apply (for example, single-operator-apparatus,multi-day precision; or multi-operator, single-day-apparatus precision),
the appropriate statistics for those systems of causes need to be developed and the appropriate combination of modifiers given in
Practice E177 should be used to describe those statistics. These should not, however, be taken as the fundamental precision
parameters for the test method. The advice of a statistical consultant should be sought in planning the interlaboratory study so that
the correct statistics can be determined.
4.3 Acceptable Range Among Results—If the test method requires more than two test results, as so defined in the method, the
difference between highest and lowest test results in the group must be compared to the maximum acceptable range for the
C670 − 24a
applicable system of causes. The range among different numbers of test results in the group, including two, that would be expected
to be exceeded with no more than about 5 % probability is obtained by multiplying the appropriate standard deviation or coefficient
of variation by the corresponding factor from the second column of Table 1. If more than two test results are obtained, the index
of precision for the difference between two results cannot be used as a criterion for judging acceptability of the differences between
pairs of results selected from the group.
4.4 Uses of Indexes of Precision
4.4.1 In Setting Specification Limits—The indexes of precision described in this practice are applicable to test results obtained on
identical test specimens and provide information on the inherent variability of the test method. In routine quality control or
acceptance testing for a project, the variation of the test results will be affected by the inherent variability of the test method, the
variability of the materials, and the variability associated with the sampling method. Specifiers need to consider these sources of
variability in setting specification limits so as to control the producer’s risk of rejection of a lot of acceptable material and the
purchaser’s risk of accepting a lot of deficient material. Practice D6607 provides a methodology for setting specification limits
that accounts for the inherent variability of the test method along with the material variability. The variability associated with the
test method may be reduced by requiring a test result to be the average of two or more test determinations. A balance, however,
needs to be achieved between the incremental cost of additional testing and the corresponding incremental reduction in uncertainty.
Also, increasing the number of determinations to obtain a test result may have a minor affecteffect on multilaboratory variability
if the between-laboratory component of variance is greater than the single-operator variance. Because specification limits should
be established with consideration of testing variability and material variability, it is not appropriate to consider the indexes of
precision of the test method as tolerances to be added to statistically-derived specification limits for the purpose of judging
acceptance or rejection of materials.
4.4.2 For Qualifying an Operator—As discussed in 4.2.1, indexes of single-operator precision are sometimes used as a basis for
qualifying an operator. The assumption is that results that do not differ by more than the stated index are indicative of proper
performance of the test. This assumption, however, is not necessarily correct. Uniform misunderstanding of instructions, incorrect
specimen preparation, or maladjustments of equipment may produce consistent but erroneous test results. Whenever possible, tests
conducted for the purpose of qualifying an operator should be made on materials for which the measured characteristic is known,
so that bias as well as precision can be evaluated. Participation in proficiency sample programs is an effective way to evaluate
operator performance among peers.
5. Basis for Precision Statement
5.1 In order to be valid, the indexes of precision to be included in the precision statement must be based on estimates of the
precision of the test method obtained from a statistically designed interlaboratory study. Before proceeding with the interlaboratory
study, the ruggedness of the test method should be investigated in accordance with Practice C1067. A ruggedness evaluation
involves the participation of a few laboratories and the use of several materials that encompass the range of the level of the
characteristics to be measured by the test method. This evaluation will provide a preliminary estimate of single-operator precision
and may indicate whether tighter tolerances are needed for key aspects of the test method. The interlaboratory study, on the other
A
TABLE 1 Maximum Acceptable Range of Test Results
Multiplier of Standard
Number of
Deviation or Coefficient
Test Results
B
of VaritationVariation
2 2.8
3 3.3
4 3.6
5 3.9
6 4.0
7 4.2
8 4.3
9 4.4
10 4.5
A
A test result can be a single determination or the average of two or more
determinations as defined in the test method.
B
Values were obtained from Table A7 of “Order Statistics and Their Use in Testing
and Estimation,” Vol 1, by Leon Harter, Aerospace Research Laboratories, United
States Air Force.
Philleo, R. E., “Establishing Specification Limits for Materials,” Cement, Concrete, and Aggregates, CCAGDP, Vol. 1, No. 2, 1979, pp. 83-87.
C670 − 24a
hand, must involve a sufficient number of laboratories, materials, and replicate measurements so that the results obtained provide
reliable estimates of the precision of the test method (Note 4). The procedures described in this practice assume that proper
estimates of precision have been obtained. Practice C802 is a companion document that describes how to organize and conduct
a suitable interlaboratory study and how to analyze the data to obtain the relevant estimates of precision.
NOTE 4—The requirement of “reliable estimates of the precision” presupposes an estimate obtained from a properly designed and executed interlaboratory
series of tests involving at least 30 degrees of freedom for single-operator standard deviation and at least 10 laboratories. See Practice C802.
5.2 The Form and Style for ASTM Standards requires that data and details of the interlaboratory study used to determine precision
and bias be filed as a research report at ASTM International Headquarters.
5.3 The ASTM International Interlaboratory Study Program (ILS) can support subcommittees in the development of precision
statements by assisting in the design of an interlaboratory study, distribution of materials or test specimens, data analysis, and
preparation of a draft research report.
5.4 A subcommittee may wish to postpone the organization of the interlaboratory study until a new test method has been approved.
In such cases, the precision statement of the new test method must include the single-operator standard-deviation (or coefficient
of variation) obtained in at least one laboratory. Preferably, the standard deviation (or coefficient of variation) should be obtained
by using materials with different levels of the characteristic being measured. A ruggedness evaluation in accordance with Practice
C1067 can be a source of data to develop a temporary precision statement. The temporary statement includes only the
single-operator standard deviation (or coefficient of variation) and does not include a difference limit (d2s or d2s%). This temporary
precision statement is permitted for five years. By the end of this period, the temporary precision statement needs to be replaced
with a complete statement based on an interlaboratory study. See Example 9 in Appendix X1.
5.5 When an approved test method is being revised, the responsible subcommittee should determine whether the proposed
change(s) to the test method will affect the validity of the precision statement in the existing standard. If the subcommittee believes
the precision of the method may be affected by the revision, a new interlaboratory study should be conducted to provide data for
updating the precision statement.
5.6 For some tests under the jurisdiction of Committees C01, C09, D04, and D18 there may be an extensive database of
interlaboratory test data obtained from various proficiency sample programs. If such data are available for a particular test method,
a precision statement can be prepared by carrying out the data analysis described in Practice C802 based upon a much larger
population of data than can normally be assembled in an interlaboratory study. Care is needed, however, in evaluating the data
because the requirement for identical test specimens may not be met by data from some proficiency sample programs. For example,
participating laboratories may be shipped the dry ingredients to prepare specimens of cementitious mixtures for testing. The
resulting specimens among the laboratories are not identical test specimens and the resulting multilaboratory precision includes
an additional source of variation associated with making the test specimens. This needs to be stated in the precision statement.
6. Form of Precision Statement
6.1 Background Information
6.1.1 Description of the Interlaboratory Study—The Form and Style for ASTM Standards requires that the precision statement
include a summary of the interlaboratory study that will permit the user of the test method to judge the reliability of the precision
statement. This summary should include the number of laboratories, number of materials, range of material characteristics
measured, and number of test determinations (replicate tests) for each material. The research report (see 5.2) should be referenced
for the details of the interlaboratory study and the data analysis leading to the precision statement. This summary information
should be provided in a note.
NOTE 5—Example 1 in Appendix X1 illustrates the wording that may be used in a note to summarize the interlaboratory study. The subcommittee should
exercise its discretion in choosing the exact w
...