ASTM F1082-00(2000)
(Practice)Standard Practice for Tires-Determining Precision for Test Method Standards (Withdrawn 2006)
Standard Practice for Tires-Determining Precision for Test Method Standards (Withdrawn 2006)
SCOPE
1.1 This practice presents guidelines for preparing clear and meaningful precision statements for test method standards on tires and related objects pertinent to the tire industry and within the scope of ASTM Committee F-9. It gives definitions, explains the potential use of precision for standard test methods and gives the requirements for interlaboratory or inter-test-site programs. The calculation algorithms for determining precision and the format for expressing precision are also given.
WITHDRAWN RATIONALE
This practice presents guidelines for preparing clear and meaningful precision statements for test method standards on tires and related objects pertinent to the tire industry and within the scope of ASTM Committee F09. It gives definitions, explains the potential use of precision for standard test methods, and gives the requirements for interlaboratory or inter-test-site programs. The calculation algorithms for determining precision and the format for expressing precision are also given.
Formerly under the jurisdiction of Committee F09 on Tires, this practice was withdrawn in 2005. This practice has been withdrawn due to lack of use in Committee F09. It is recommended that Practice E 691, the generic standard for precision in ASTM, and Practice D 4483, the precision standard for Committee D11 on Rubber, be consulted by anyone in Committee F09 who requires guidance on evaluating precision for any test method standard in F09.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard's Document Summary page on the ASTM website.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:F1082 –00 (Reapproved 2000)
Standard Practice for
Tires—Determining Precision for Test Method Standards
This standard is issued under the fixed designation F1082; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Knowing the precision (and where possible the bias and accuracy, or both) of test measurements is
vital for efficient technical decision making in any area of technology. For many years the chemical
and allied material industries have addressed the issue of test precision, especially as it applies to
inter-laboratory testing. Test method precision is important in the tire industry as well.
Some of the specific details that are important in laboratory testing frequently do not apply when
objects such as tires are tested, especially when tested for various performance features at proving
grounds or with other outdoor test methods. However, the basic methodology of “within” and
“between” laboratory test precision assessment can be applied to tire testing provided the unique
characteristics of some tire tests are kept in mind. This practice gives broad guidelines for tire test
precision assessment.
When special test requirements arise that differ from the more orthodox precision methodology,
they will have to be addressed in a special “ad hoc” manner. As experience is gained with these
“special cases”, the procedures for handling them can be formalized and incorporated into this
practice.
1. Scope 3.1.1 accuracy, n—a measurement concept that describes
the degree of correspondence between an average measured
1.1 Thispracticepresentsguidelinesforpreparingclearand
value and an accepted reference or standard value for the
meaningful precision statements for test method standards on
object, material or phenomenon under test.
tiresandrelatedobjectspertinenttothetireindustryandwithin
3.1.1.1 Discussion—The reference value may be estab-
the scope of ASTM Committee F-9. It gives definitions,
lished by theory, by reference to an accepted standard, to
explainsthepotentialuseofprecisionforstandardtestmethods
anothertestmethod,orinsomecasestheaveragethatcouldbe
and gives the requirements for interlaboratory or inter-test-site
obtained by applying the test method to all of the sampling
programs. The calculation algorithms for determining preci-
units comprising a lot.
sion and the format for expressing precision are also given.
3.1.2 bias, n—the difference between the average measured
2. Referenced Documents test result and the accepted reference value; it measures in an
inverse manner the accuracy of a test.
2.1 ASTM Standards:
3.1.2.1 Discussion—Alargebiasimpliespooraccuracy,and
E691 Practice for Conducting an Interlaboratory Study to
a small or negligible bias denotes a high accuracy; when bias
Determine the Precision of a Test Method
exists,increasedtestingdoesnotincreaseaccuracy,butmerely
F538 Terminology Relating to the Characteristics and Per-
gives an increased confidence in the bias estimate.
formance of Tires
3.1.3 determination, n—the application of the complete
3. Terminology
measurement procedure to one piece, specimen or object to
produce one numerical measured value to be used to form an
3.1 Definitions of Terms
average or median.
3.1.4 precision, n—a measurement concept that expresses
This practice is under the jurisdiction ofASTM Committee F09 onTires and is
the ability to generate test results that agree with each other in
the direct responsibility of Subcommittee F09.10 on Equipment, Facilities, and
absolute magnitude.
Calibration.
Current edition approved May 10, 2000. Published July 2000. Originally
published as F1082–87. Last previous edition F1082–93.
Annual Book of ASTM Standards, Vol 14.02.
Annual Book of ASTM Standards, Vol 09.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F1082
3.1.4.1 Discussion—The degree of agreement is normally 4.1.2 Those that are fully developed and are in routine use
measured inversely by the standard deviation, high precision as Committee F-9 test method standards.
correspondstoalow(small)standarddeviation.Highprecision 4.2 Generaltheoryisincludedtobetterunderstandthebasis
may exist simultaneously with a large bias or poor accuracy. of precision calculations (See Section 7 andAnnexA1,Annex
3.1.5 repeatability,r, n—an established value, below which A2, andAnnexA4). For those who have a familiarity with this
the absolute difference between two “within-laboratory” or theoretical basis and for those engaged in frequent precision
“within test-site” test results may be expected to lie, with a calculations, the computational formulas in Annex A4 will
specified probability. prove helpful.
3.1.5.1 Discussion—The two test results are obtained with
5. General Principles
the same method on nominally identical test materials under
5.1 Although detailed definitions for repeatability and re-
the same conditions (same operator, apparatus, laboratory,
producibility are given later in this practice, a few words of
location,andspecifiedtimeperiod),andintheabsenceofother
general discussion are merited at this point.
indications,thespecifiedprobabilityis0.95(sometimeswritten
5.1.1 Repeatability refers to the ability of the same labora-
as95%).The“establishedvalue”alsomaybecalleda“critical
tory or testing apparatus to obtain similar (test) results under
difference.”
certain specified conditions. Reproducibility refers to the
3.1.6 repeatability, relative (r), n—a repeatability estimate
ability of different laboratories or testing apparatus in different
expressed as a percentage of the average of the property for
locations to obtain similar test results under certain specified
which the estimate was obtained.
conditions. If test results closely agree, then good repeatability
3.1.6.1 Discussion—It is often appropriate to express re-
or good reproducibility exists.
peatability on a relative basis, as a percent of a mean value.
5.2 The precision of a test method does not of necessity
This form is similar to a coefficient of variation. Such expres-
characterize a test with regard to how sensitive it is in
sion is useful when r varies with the average level of the
measuring the basic property it is intended to measure. Preci-
property being measured. Relative values for r cannot be
sionmaybegoodsimplybecausethetestmethodisinsensitive
unambiguously expressed as percentage (%) alongside the
to the basic property it measures. A concept called“ test
actual measured values in usual test result units because some
sensitivity” has been defined in the statistical literature as the
test methods have “percent” as their unit. To avoid this
ratio of the responsiveness of the test measurement to finite
ambiguity, the symbol (r) is used.
variations in the basic property in question to the precision of
3.1.7 reproducibility, R, n—an established value, below
the measurement. This practice does not address this issue.
which the absolute difference between two“ between-
5.3 Both repeatability and reproducibility should be deter-
laboratory” or “between test-site” test results may be expected
mined under realistic or typical laboratory or test site condi-
to lie, with a specified probability.
tions. If extraordinary care is exercised in the laboratory, the
3.1.7.1 Discussion—The two test results are obtained with
precision statement may be overly optimistic.
the same method on nominally identical test materials under
5.3.1 The reported value of repeatability normally quoted
differentconditions(differentlaboratories,locations,operators,
will include the sum of the two components of variability. As
apparatusandinaspecifiedtimeperiod),andintheabsenceof
ordinarily determined, repeatability has both a test apparatus
other indications, the specified probability is 0.95. The essen-
variability and any test object variability that cannot be
tial characteristic of reproducibility is the variability of the
physically removed. Object variability that is not inherent in
different laboratories or test sites in which the testing is
the overall operation of the test may be removed if an
conducted.
appropriate test program is conducted and a statement is
3.1.8 reproducibility, relative (R), n— a reproducibility
included with the reported value of precision.
estimateexpressedaspercentageoftheaverageoftheproperty
5.4 Discussion of Repeatability (Very Short, Short, Long
for which the estimate was obtained.
Term):
3.1.8.1 Discussion—Itisoftenappropriatetoexpressrepro-
5.4.1 There are at least three different viewpoints that have
ducibilityonarelativebasis,asapercentofameanvalue.This
been expressed with regard to repeatability.
form is similar to a coefficient of variation. Such expression is
5.4.1.1 View 1—The smallest possible or “very short” time
useful when R varies with the average level of the property
period is used to estimate the variation. The same material,
being measured. Relative values for R cannot be unambigu-
apparatus and operator is used and repeat determinations are
ously expressed as percentages (%) alongside the actual
made within a period measured in minutes or at most within a
measured values in usual test result units because some test
period measured in hours.
methodshave“percent”astheirunits.Toavoidthisambiguity,
5.4.1.2 View 2—A “short” time period is used for the
the symbol (R) is used.
repeatedoperationsthatproducetestresults.Thesamematerial
3.1.9 test result, n—the average or median of a specified
and same operator (or set of operators) is employed but the
number of determinations; it is the reported value for a test.
time period for the repeat operations is most frequently
4. Significance and Use
measured in days.
4.1 This practice applies to the following test method 5.4.1.3 View 3—A “long term” time period is used for the
standards: repeated operations that produce test results within a labora-
4.1.1 Those that have test results expressed in terms of a tory. This may be weeks or months. Although it may be
quantitative continuous variable. possible to use the same material, different operators are often
F1082
employed and due to the long-term nature certain other necessary to ensure that the supply of objects available is
changes such as recalibration of the test apparatus may have sufficient to cover the experiment and keep a stock in reserve.
taken place. These changed conditions produce increased 6.2.5 At each level, p separate containers (the number of
variability. laboratories or sites) should be used where there is any danger
5.4.2 The time period must be specified as each particular of the objects changing or material deteriorating when the
test method standard is taken up for consideration. container has once been opened. Special instructions on
storage and treatment should be prescribed.
6. Organizing a Precision Estimation Program
6.3 Actual Organization of the Tests:
6.1 Task Group—Ataskgroupofqualifiedpeopleshouldbe
6.3.1 TheinterlaboratorytestplanisshowninFig.1,atable
organized to conduct the program; a chairman, a statistical
that indicates the laboratories or locations, materials or objects
expert and members well-experienced with the standard in
andreplicates.Withqlevelsandnreplicates,eachparticipating
question. The panel chairman should ensure that all instruc-
laboratory or test site among the p total has to carry out qn
tions of the program are clearly communicated to all labora-
tests. A decision is necessary (for each test standard) as to
tories or test locations in the program.
whether a “replicate” is to be a “determination” or a “test
6.2 Laboratories, Test Sites, and Materials or Objects:
result” as defined in this document. The performance of these
6.2.1 The number of laboratories, test locations or sites
tests should be organized and the operators instructed as
should be determined. The number of test objects, each
follows:
comprising a different level of the measured property, should
6.3.2 All q·ntestsshouldbeperformedbyoneandthesame
be selected.
operatororoperatorset,usingthesameequipmentthroughout.
6.2.1.1 Atleasttenparticipatinglaboratoriesortestsitesare
6.3.3 Each group of n tests belonging to one level must be
recommended.Aprogramthatinvolvesfewerthansixmaynot
performed under repeatability conditions, in a specified inter-
lead to reliable estimates of the reproducibility of the test
val of time.
method.
6.3.4 Itisessentialthatagroupof ntestsunderrepeatability
6.2.2 The number and type of objects (materials) to be
conditions be performed independently as if they were n tests
included will depend on the following:
on different materials.
6.2.2.1 The range of the property and how precision varies
6.3.5 The number of replicates n, must be specified. Each
over that range,
replicatemaybe onetestresultor onedeterminationaccording
6.2.2.2 The different types of objects to which the test
to the requirements of the test method standard. Normally, n is
method is applied,
two, but it may be larger.
6.2.2.3 The difficulty (expense) in performing the tests, and
6.4 Instructions to Operators—The operators should re-
6.2.2.4 The commercial or legal need for obtaining a reli-
ceivenoinstructionsotherthanthosecontainedinthestandard
able estimate of precision.
should be asked to comment on the standard and state whether
6.2.3 For each level or class of object an adequate quantity
the instructions contained in it are sufficiently clear. All
(sample) of homogeneous objects should be available for
participating laboratories or test sites should report their test
subdivision and distribution by random allocation to the
results to one more significant figure than is customary or
participating laboratories. The term “objects” is used in a
prescribed in the Standard.
broad, generic sense. When the objects to be tested are not
6.5 Reporting the Test Results—Each laboratory or test site
homogeneous, it is important to obtain or prepare the samples
supervisor should write a full report containing the following
in a well-documented manner.
particulars:
6.2.3.1 Since object or material variability is included when
6.5.1 The final test results, (avoid transcription and typing
measuring test variability, objects with high inherent variation
errors).
will cause the test to appear insensitive. High precision with
6.5.2 The original individual observations or determination
large bias seems to frequently occur in destructive tire tests. It
values from which the final results were derived.
is desirable
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