ASTM D3244-97(2002)
(Practice)Standard Practice for Utilization of Test Data to Determine Conformance with Specifications
Standard Practice for Utilization of Test Data to Determine Conformance with Specifications
SCOPE
1.1 This practice covers guidelines with which two parties, usually a supplier and a receiver, can compare and combine independently obtained test results whenever there is a product quality dispute.
1.2 This practice defines a technique for comparing an assigned test value with a specification limit.
1.3 This practice applies only to those test methods which specifically state that the repeatability and reproducibility values conform to the definitions herein.
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Standards Content (Sample)
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An American National Standard
Designation: D 3244 – 97 (Reapproved 2002)
Standard Practice for
Utilization of Test Data to Determine Conformance with
Specifications
This standard is issued under the fixed designation D3244; 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
The properties of commercial petroleum products are measured by standardized laboratory test
methods to check their conformance to specifications. Two or more measurements of the same
propertyofaspecificsamplebyanygiventestmethodusuallywillnotgivepreciselythesameanswer.
Therefore, the test methods generally include a paragraph on the precision of results. This precision
is an expression of the reliability of the value of the measured property.
Manydifficultiesthatariseininterpretingspecificationsareduetotestimprecision.Becauseofthis,
a true value of a property can never be determined exactly; and it is necessary to infer from measured
values the range within which the “true value” is likely to lie. The main purpose of this practice is to
indicate how test imprecision should be interpreted relative to specification values.
1. Scope 2.2 ISO Standard:
ISO 4259 Determination andApplication of Precision Data
1.1 This practice covers guidelines with which two parties,
in Relation to Methods of Test
usually a supplier and a receiver, can compare and combine
independentlyobtainedtestresultswheneverthereisaproduct
3. Terminology
quality dispute.
3.1 Definitions:
1.2 This practice defines a technique for comparing an
3.1.1 acceptance limit (AL), n—a numerical value that
assigned test value with a specification limit.
defines the point between acceptable and unacceptable quality.
1.3 This practice applies only to those test methods which
3.1.1.1 Discussion—The AL is not necessarily the specifi-
specifically state that the repeatability and reproducibility
cation limit. It is a value that takes into account the specifica-
values conform to the definitions herein.
tion value, the test method precision, and the confidence level
2. Referenced Documents desiredfordefiningminimumacceptablequalityrelativetothe
specification value.
2.1 ASTM Standards:
3.1.2 assignedtestvalue(ATV),n—theaverageofallresults
D1319 Test Method for Hydrocarbon Types in Liquid
obtained in the several laboratories which are considered
Petroleum Products by Fluorescent Indicator Adsorption
acceptable based on the reproducibility of the test method.
D4057 Practice for Manual Sampling of Petroleum and
3.1.3 determination, n—the process of carrying out the
Petroleum Products
series of operations specified in the test method whereby a
D4177 Practice for Automatic Sampling of Petroleum and
single value is obtained.
Petroleum Products
3.1.4 dispute, n—when there is a question as to product
E29 Practice for Using Significant Digits in Test Data to
quality because a test value obtained falls outside the accep-
Determine Conformance with Specifications
tance limit.
3.1.5 operator, n—a person who normally and regularly
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum carries out a particular test.
ProductsandLubricantsandisthedirectresponsibilityofSubcommitteeD02.94on
3.1.6 precision, n—thedegreeofagreementbetweentwoor
Quality Assurance and Statistics.
more results on the same property of identical test material. In
Current edition approved Dec. 10, 2002. Published March 2003. Originally
publishedasanappendixtothe1968AnnualBookofASTMStandards,Part18.Last
previous edition approved in 1997 as D3244–97.
Annual Book of ASTM Standards, Vol 05.01.
3 5
Annual Book of ASTM Standards, Vol 05.02. Available from American National Standards Institute, 25 W. 43nd St., 4th
Annual Book of ASTM Standards, Vol 14.02. floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 3244 – 97 (2002)
this practice, precision statements are framed in terms of the 4.1.1 This practice can be used to ensure that such proper-
repeatability and reproducibility of the test method. tiesarecorrectlystatedonlabelsorinotherdescriptionsofthe
3.1.7 receiver, n—any individual or organization who re- product.
ceives or accepts the product delivered by the supplier. 4.1.2 Thispracticecanbeimplementedinthosecaseswhere
3.1.8 repeatability (r), n—quantitative expression of the a supplier uses a commercial testing laboratory to sample and
random error associated with a single operator in a given test a product prior to releasing the product to a shipper
laboratory obtaining replicate results with the same apparatus (intermediate receiver) and the ultimate receiver also uses a
under constant operating conditions on identical test material commercial testing laboratory to sample and test the product
within a short period of time. It is defined (3.1.8.1) as that upon arrival at the destination. The assigned test value (ATV)
difference between two such single results as would be would still be determined according to 8.3.
exceededinthelongruninonly1casein20inthenormaland 4.2 This practice can also assist in the determination of
correctoperationofthetestmethod(3.1.8.3).(Thisisknownas proper tolerances which will ensure that the actual value of a
the 95% confidence level.) property is sufficiently close to the specification value so that
3.1.8.1 Discussion—The repeatability and reproducibility the product is acceptable to the receiver. Such tolerances are
values should have been determined according to the methods bounded by an acceptance limit (AL). If the value determined
described in ASTM Research Report RR:D02-1007, Manual bytesting(assignedtestvalue,(ATV))fallsontheALoronthe
on Determining Precision data for ASTM Methods of Petro- acceptable side of the AL, the product can be accepted;
leum Products and Lubricants or ISO 4259. otherwise it must be rejected.
3.1.8.2 Discussion—Not all standards organizations define 4.3 Both parties must agree in advance on setting the AL
repeatability and reproducibility in precisely these same terms, and on how the ATV is to be calculated.
and attention should always be paid to definitions before 4.3.1 This agreement should include a decision as to
comparing precision values quoted. whether the test values are to be determined by the absolute or
3.1.8.3 Discussion—This difference is related to the repeat- rounding-off method of Practice E29, as therein defined.
ability or the reproducibility standard deviation but is not the 4.3.1.1 Iftherounding-offmethodistobeused,thenumber
standard deviation. of significant digits to be retained must also be agreed upon.
3.1.9 reproducibility (R), n—quantitative expression of the 4.3.1.2 Thesedecisionsmustalsobemadeinthecasewhere
random error associated with operators working in different only one party is involved, as in the case of a label.
laboratories, each obtaining single results on identical test 4.4 This practice is designed to be suitable for reference in
materialwhenapplyingthesamemethod.Itisdefined(3.1.8.1) contracts governing the transfer of petroleum products and
as that difference between two such single and independent lubricants from a supplier to a receiver.
results as would be exceeded in the long run in only 1 case in 4.5 Application of this practice requires the designation of
20 in the normal and correct operation of the test method. See each limit of each property of a specification as “critical” or
3.1.8.3. “noncritical” at a desired probability level, as defined in this
3.1.10 result, n—the value obtained by following the com- practice.
plete set of instructions of a test method. It may be obtained 4.6 Asaprerequisiteforacceptanceforlabtestresultstobe
fromasingledeterminationorseveraldeterminations,depend- usedinthispractice,thefollowingconditionsshallbesatisfied:
ing on the instruction of the test method. 4.6.1 Long-term standard deviation for the appropriate test
3.1.11 supplier, n—any individual or organization respon- method(s) from each lab, as substantiated by in-house quality
sible for the quality of a product just before it is taken over by controlprograms,onmaterialtypicaloftheproductindispute,
the receiver. shall be statistically equivalent or better than the published
3.1.12 test sample, n—a portion of the product taken at the method standard deviation under reproducibility conditions.
place where the product is exchanged, that is, where the 4.6.2 Each lab shall be able to demonstrate, by way of
responsibility for the product quality passes from the supplier results from interlaboratory exchange programs, a lack of a
to the receiver. Actually, this is rarely possible and a suitable statistically significant bias relative to exchange averages for
sampling location should be mutually agreed upon. the appropriate test method(s).
3.1.13 true value (µ), n—for practical purposes, the value 4.6.3 In the event that the long-term standard deviation for
towards which the average of single results obtained by N any party’s laboratory is not statistically equivalent, then, for
laboratories tends, when N becomes very large (3.1.13.1). thepurposeofestablishingtheassignedtestvalue(ATV),each
Consequently, such a true value is associated with the particu- laboratory’s test result(s) shall be inversely weighted in accor-
lar test method employed. dance with laboratory’s demonstrated variance(s).
3.1.13.1 Discussion—It is recognized that there are cases 4.7 It is recommended that this practice be conducted under
where a true value not equal to the method average can exist. the guidance of a qualified statistician.
As used in this practice, the method average value is intended
5. Sampling
to mean “true value” even if the method is biased.
5.1 Sampling should be carried out in accordance with
4. Significance and Use
standardsamplingproceduresforpetroleumproducts(Practice
4.1 This practice provides a means whereby the parties to a D4057 and Practice D4177). Obtain enough sample to allow
transaction can resolve potential disputes over those product all required determinations to be made. Divide the sample into
properties which can be tested and expressed numerically. three secondary samples: a receiver sample, a supplier sample,
D 3244 – 97 (2002)
and a retain sample. The retain sample should itself be large by 1.2 (to convert a range for two to a range for three) and
enoughtopermitfurthersubdivisionintothreeportionsincase compare this value with the difference between the two
additional test work is desirable. extreme results for acceptance. If acceptance is indicated, the
assignedtestvalue(ATV)forthesampleshouldbetheaverage
6. Applying Precision Data to Test Methods
of the three results.
6.1 Thissectiondescribesproceduresinwhichtheprecision
7. Applying Precision Data to Specifications
limits of test methods may be used to indicate when results
obtained by two laboratories differ significantly. This section
7.1 Specifications—Aspecification fixes a limit to the true
mayalsobeusedforrejectionofresultsofreplicatetestsbyan value of a given property. In practice, however, this true value
operator.
can never be established exactly. The property is measured in
6.2 Significance of Repeatability (r): thelaboratorybyapplyingastandardtestmethod,theresultsof
6.2.1 Acceptance of Results—When only two results are
which may show some scattering as defined by the repeatabil-
obtained under conditions of repeatability and the difference is ity and reproducibility limits. There is always, therefore, some
equal to or less than the repeatability of the method, the
uncertainty as to the true value of the tested property.
operator may report the average of the two results as being 7.2 Although the true value is never known exactly, the
applicable to the sample tested.
probability of obtaining any specific test result, relative to the
6.2.2 Rejection of Results—When two results are obtained
true value, can be calculated if the probability distribution
that differ by more than the repeatability of the method, both
functionforthetestmethodisknown(forexample,thenormal
should be rejected. Obtain two additional results immediately
distribution curve with its associated reproducibility).
under conditions of repeatability. If the difference between
7.2.1 Somespecifications,becauseoftheproductcharacter-
thesetworesultsisequaltoorlessthantherepeatabilityofthe
istic or the end use of the product, or both, require that the
method, the operator should report the average of the two as
receiver have a high degree of assurance that the product
being applicable to the sample tested. If, however, the differ-
actually meets or exceeds the quality level indicated by the
ence so obtained again exceeds the repeatability, reject the
specification value. For the purpose of this practice, such
results and investigate the application of the method.
specifications are called critical specifications.
6.3 Significance of Reproducibility (R):
7.2.2 Specifications that require assurance only that the
6.3.1 Acceptance of Results—When two results are ob-
product quality is not substantially poorer than is indicated by
tained in different laboratories (Note 1) and the difference is the specification level are called noncritical specifications for
equal to or less than the reproducibility of the method, both
the purposes of this practice.
results should be considered acceptable. The value assigned to 7.3 Specification Conformance Guidelines:
the sample should be the average of the two results.
7.3.1 Whenever a product is tested for conformity to a
specification, a decision must ultimately be made as to the
NOTE 1—When a comparison for reproducibility is made between
acceptance or rejection of the product.
results from two laboratories, it is assumed that single results from each
7.3.2 The numerical value that divides the regions of
will be compared. If each of the laboratories has produced more than a
single result, see 6.4.
acceptable and unacceptable product test values is the accep-
tance limit (AL). The AL may or may not coincide with the
6.3.2 Rejection of Results—When the results from two
specification value (S) used to define a product quality or
laboratories differ by more than the reproducibility of the
grade.
method, reject both results and each laboratory should repeat
7.3.3 The AL value, which must be agreed upon by the
the test on the retained sample. If the difference is now equal
supplier and receiver, is that level of quality such that, if the
to or less than the reproducibility, both res
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