ASTM D6631-05(2011)
(Guide)Standard Guide for Committee D01 for Conducting an Interlaboratory Study for the Purpose of Determining the Precision of a Test Method
Standard Guide for Committee D01 for Conducting an Interlaboratory Study for the Purpose of Determining the Precision of a Test Method
SIGNIFICANCE AND USE
The purpose of an interlaboratory evaluation, as defined in this guide, is to determine the variability of results obtained in different laboratories on equivalent equipment using a prescribed test method.
The definitions of statistical terms used in this guide are contained in Terminology E456.
SCOPE
1.1 This guide covers a simplified statistical procedure for planning and conducting interlaboratory evaluations of test methods.
General Information
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Standards Content (Sample)
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Designation: D6631 − 05 (Reapproved2011)
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 fail), or ordered (ranked), present three special problems in the
creation of a meaningful precision statement:
1.1 This guide covers a simplified statistical procedure for
4.1.1 The amount of information contained in discrete and
planning and conducting interlaboratory evaluations of test
ordereddataismuchlessthanincontinuousdata,necessitating
methods.
the collection of much more data.
4.1.2 The sensitivity (the ability to discriminate between
2. Referenced Documents
similar samples) is much less in discrete and ordered data than
2.1 ASTM Standards:
continuous data.
E177 Practice for Use of the Terms Precision and Bias in
4.1.3 Since the precision statement relies on the normal
ASTM Test Methods
distribution, and the distributions of discrete and ordered data
E456 Terminology Relating to Quality and Statistics
are usually decidedly non-normal, the normal precision state-
E691 Practice for Conducting an Interlaboratory Study to
ment is invalid.
Determine the Precision of a Test Method
4.2 Given these concerns with discrete and ordered data, a
E1345 Practice for Reducing the Effect of Variability of
simple statement of the results obtained in these types of
Color Measurement by Use of Multiple Measurements
studies might be the most useful information for a prospective
user of a test method.
3. Significance and Use
3.1 The purpose of an interlaboratory evaluation, as defined
5. Preliminary
in this guide, is to determine the variability of results obtained
5.1 Flow chart the test method.
in different laboratories on equivalent equipment using a
prescribed test method.
5.2 Survey known sources of information related to the test
3.2 The definitions of statistical terms used in this guide are method to establish how results are affected by variations in
operating conditions, atmospheric conditions, differences be-
contained in Terminology E456.
tween operators, etc. Select what appears to be the optimum
4. Problem Formulation procedure.
4.1 The objective of the evaluation should be to clearly 5.3 Provide instructions for the test method and, without
define the expected precision of the test method. Within the
comment, observe a laboratory technician perform a test
current limits of both the software, and the statistical protocols according to these instructions. Revise any parts of the draft
currently available, this effectively restricts the use of this
causing difficulty.
guide to test methods which yield results that are continuous.
5.4 If desirable, make a comparative study with other test
This generally means a measured quantity, such as pH or
methods for measuring the property by using specimens with a
brightness. Results that are discrete (such as counts or pass-
wide range of values of the property under test (and possibly
with wide ranges in other properties).
This guide is under the jurisdiction of ASTM Committee D01 on Paint and
6. Preparation for Interlaboratory Study
Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.20 on Quality Assurance and Statistics.
6.1 Prepare a clear statement of the type of information
Current edition approved June 1, 2011. Published June 2011. Originally
required from the interlaboratory evaluation.
approved in 2001. Last previous edition approved in 2005 as D6631 – 05. DOI:
10.1520/D6631-05R11.
6.2 Based on the study made in one laboratory (Section 5),
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
prepare a proposed master plan for the interlaboratory evalu-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ation. Discuss the plan, in an open meeting, if possible, with
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. other participants in the study.
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D6631 − 05 (2011)
6.3 Select the materials to be used in the interlaboratory ample, rotational and efflux cup viscometers, must NOT be
evaluations so as to: used in the same study.
6.3.1 Cover the applicable range of the property or compo-
10.1.4 Replicates—Each evaluation must at least be run in
nent to be measured, and
duplicate.
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
7.1 If the test method is new or the procedure for an old test
“blind” repetition. In this procedure two samples of at least
method is greatly altered, a pilot study by one laboratory
one,andpreferablymore,ofthetestmaterialsaredistributedas
involving a few materials (two or three) may reveal seriously
separate materials. If all the materials are duplicated, the total
misleading directions in the written procedure. A Box and
amount of work can be kept the same by not repeating the test
Whisker Plot (as outlined in Practice E1345), or a Violin Plot
at another time. However, elimination of the time variable
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 study be aware of the capability of
usually very good, two repeats each in duplicate are often
thoseparticipantstorunthemethodunderstudy.Thisisnotthe
sufficient.However,owingtothemuchmorevariablenatureof
responsibility of the originator of the study, or ASTM. A Box
measurements of the physical or application test properties, the
and Whisker Plot will also be helpful in this qualification
repeats should be increased, unless it
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