ASTM D6631-01

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Designation:D6631–01
Standard Guide for
Committee D01 for Conducting an Interlaboratory Study,
and Determining the Precision of a Test Method
This standard is issued under the fixed designation D 6631; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4.1.1 The amount of information contained in discrete and
ordered data is much less than in continuous data, necessitating
1.1 This guide covers a simplified statistical procedure for
the collection of much more data.
planning and conducting interlaboratory evaluations of test
4.1.2 The sensitivity (the ability to discriminate between
methods.
similar samples) is much less in discrete and ordered data than
2. Referenced Documents continuous data.
4.1.3 Since the precision statement relies on the normal
2.1 ASTM Standards:
distribution, and the distributions of discrete and ordered data
E 177 Practice for Use of the Terms Precision and Bias in
are usually decidedly non-normal, the normal precision state-
Test Methods
ment is invalid.
E 456 Terminology for Relating to Quality and Statistics
4.2 Given these concerns with discrete and ordered data, a
E 691 Practice for Conducting an Interlaboratory to Deter-
simple statement of the results obtained in these types of
mine the Precision of a Test Method
studies might be the most useful information for a prospective
E 1345 Practice for Reducing the Variability of Color Mea-
user of a test method.
surements by Use of Multiple Measurements
5. Preliminary
3. Significance and Use
5.1 Flow chart the test method.
3.1 The purpose of an interlaboratory evaluation, as defined
5.2 Survey known sources of information related to the test
in this guide, is to determine the variability of results obtained
method to establish how results are affected by variations in
in different laboratories on equivalent equipment using a
operating conditions, atmospheric conditions, differences be-
prescribed test method.
tween operators, etc. Select what appears to be the optimum
3.2 The definitions of statistical terms used in this guide are
procedure.
contained in Terminology E 456.
5.3 Provide instructions for the test method and, without
4. Problem Formulation
comment, observe a laboratory technician perform a test
according to these instructions. Revise any parts of the draft
4.1 The objective of the evaluation should be to clearly
causing difficulty.
define the expected precision of the test method. Within the
5.4 If desirable, make a comparative study with other test
current limits of both the software, and the statistical protocols
methods for measuring the property by using specimens with a
currently available, this effectively restricts the use of this
wide range of values of the property under test (and possibly
guide to test methods which yield results that are continuous.
with wide ranges in other properties).
This generally means a measured quantity, such as pH or
brightness. Results that are discrete (such as counts or pass-
6. Preparation for Interlaboratory Study
fail), or ordered (ranked), present three special problems in the
6.1 Prepare a clear statement of the type of information
creation of a meaningful precision statement:
required from the interlaboratory evaluation.
6.2 Based on the study made in one laboratory (Section 5),
prepare a proposed master plan for the interlaboratory evalu-
This guide is under the jurisdiction of ASTM Committee D01 on Paint and
Related Coatings, Materials, and Applications and is the direct responsibility of
ation. Discuss the plan, in an open meeting, if possible, with
Subcommittee D01.20 on Quality Assurance and Statistics.
other participants in the study.
Current edition approved Feb. 10, 2001. Published April 2001.
2 6.3 Select the materials to be used in the interlaboratory
Annual Book of ASTM Standards, Vol 14.02.
Annual Book of ASTM Standards, Vol 06.01. evaluations so as to:
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D6631
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 E 1345), 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 has been decided to use
protocol. atestmethodmainlyforrankingaseriesofm
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