ASTM D6631-05(2023)

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: D6631 − 05 (Reapproved 2023)
Standard Guide for
Committee D01 for Conducting an Interlaboratory Study for
the Purpose of Determining the Precision of a Test Method
This standard is issued under the fixed designation D6631; 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.
1. Scope current limits of both the software, and the statistical protocols
currently available, this effectively restricts the use of this
1.1 This guide covers a simplified statistical procedure for
guide to test methods which yield results that are continuous.
planning and conducting interlaboratory evaluations of test
This generally means a measured quantity, such as pH or
methods.
brightness. Results that are discrete (such as counts or pass-
1.2 This international standard was developed in accor-
fail), or ordered (ranked), present three special problems in the
dance with internationally recognized principles on standard-
creation of a meaningful precision statement:
ization established in the Decision on Principles for the
4.1.1 The amount of information contained in discrete and
Development of International Standards, Guides and Recom-
ordered data is much less than in continuous data, necessitating
mendations issued by the World Trade Organization Technical
the collection of much more data.
Barriers to Trade (TBT) Committee.
4.1.2 The sensitivity (the ability to discriminate between
similar samples) is much less in discrete and ordered data than
2. Referenced Documents
continuous data.
2.1 ASTM Standards:
4.1.3 Since the precision statement relies on the normal
E177 Practice for Use of the Terms Precision and Bias in
distribution, and the distributions of discrete and ordered data
ASTM Test Methods
are usually decidedly non-normal, the normal precision state-
E456 Terminology Relating to Quality and Statistics
ment is invalid.
E691 Practice for Conducting an Interlaboratory Study to
4.2 Given these concerns with discrete and ordered data, a
Determine the Precision of a Test Method
simple statement of the results obtained in these types of
E1345 Practice for Reducing the Effect of Variability of
studies might be the most useful information for a prospective
Color Measurement by Use of Multiple Measurements
user of a test method.
3. Significance and Use
5. Preliminary
3.1 The purpose of an interlaboratory evaluation, as defined
5.1 Flow chart the test method.
in this guide, is to determine the variability of results obtained
in different laboratories on equivalent equipment using a
5.2 Survey known sources of information related to the test
prescribed test method.
method to establish how results are affected by variations in
operating conditions, atmospheric conditions, differences be-
3.2 The definitions of statistical terms used in this guide are
tween operators, etc. Select what appears to be the optimum
contained in Terminology E456.
procedure.
4. Problem Formulation
5.3 Provide instructions for the test method and, without
4.1 The objective of the evaluation should be to clearly comment, observe a laboratory technician perform a test
define the expected precision of the test method. Within the according to these instructions. Revise any parts of the draft
causing difficulty.
1 5.4 If desirable, make a comparative study with other test
This guide is under the jurisdiction of ASTM Committee D01 on Paint and
Related Coatings, Materials, and Applications and is the direct responsibility of methods for measuring the property by using specimens with a
Subcommittee D01.20 on Quality Assurance and Statistics.
wide range of values of the property under test (and possibly
Current edition approved Dec. 1, 2023. Published December 2024. Originally
with wide ranges in other properties).
approved in 2001. Last previous edition approved in 2019 as D6631 – 05 (2019).
DOI: 10.1520/D6631-05R23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 6. Preparation for Interlaboratory Study
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
6.1 Prepare a clear statement of the type of information
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. required from the interlaboratory evaluation.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6631 − 05 (2023)
6.2 Based on the study made in one laboratory (Section 5), reproducibility. (It must be emphasized that the word “differ-
prepare a proposed master plan for the interlaboratory evalu- ent” in this section, could apply to multiple manufacturers, or
ation. Discuss the plan, in an open meeting, if possible, with models of equipment.) However, different equipment, using
other participants in the study. different techniques or protocols for measurement, for
example, rotational and efflux cup viscometers, must NOT be
6.3 Select the materials to be used in the interlaboratory
used in the same study.
evaluations so as to:
10.1.4 Replicates—Each evaluation must at least be run in
6.3.1 Cover the applicable range of the property or compo-
duplicate.
nent to be measured, and
6.3.2 Represent as many classes of materials as feasible, to
10.2 Intralaboratory Precision is usually ascertained by
which the test method will be applied. having repeats made over the shortest possible time, preferably
the same day. If considered desirable, a completely unbiased
7. Pilot Evaluation
estimate of intralaboratory error can be obtained by use of
“blind” repetition. In this procedure two samples of at least
7.1 If the test method is new or the procedure for an old test
method is greatly altered, a pilot study by one laboratory one, and preferably more, of the test materials are distributed as
separate materials. If all the materials are duplicated, the total
involving a few materials (two or three) may reveal seriously
misleading directions in the written procedure. A Box and amount of work can be kept the same by not repeating the test
at another time. However, elimination of the time variable
Whisker Plot (as outlined in Practice E1345), or a Violin Plot
may help to clarify this evaluation. might alert cooperators to the use of blind repetition which, in
any event, is not readily applicable when all the test materials
8. Participating Laboratory Qualification
differ markedly in properties.
8.1 It is important that the managers of proposed partici-
10.3 For analytical test methods, the precision of which is
pants in an interlaboratory stu
...