ASTM D2906-97(2002)
(Practice)Standard Practice for Statements on Precision and Bias for Textiles (Withdrawn 2008)
Standard Practice for Statements on Precision and Bias for Textiles (Withdrawn 2008)
SCOPE
1.1 This practice serves as a guide for using the information obtained as directed in Practice D 2904 or obtained by other statistical techniques from other distributions, to prepare statements on precision and bias in ASTM methods prepared by Committee D-13. The manual on form and style for standards specifies that statements on precision and bias be included in test methods. Committee D-13 recommends at least a statement about single-operator precision in any new test method, or any test method not containing a precision statement that is put forward for 5-year approval, in both instances with a complete statement at the next reapproval. If a provisional test method is proposed, at least a statement on single-operator precision is expected.
1.2 The preparation of statements on precision and bias requires a general knowledge of statistical principles including the use of components of variance estimated from an analysis of variance. Instructions covering such calculations are available in Practice D 2904 or in any standard text (1,2,3,4, and 5).
1.3 The instructions in this practice are specifically applicable to test methods in which test results are based ( 1) on the measurement of variables, (2) on the number of successes or failures in the specified number of observations, (3) on the number of defects or incidents counted in a specified interval or in a specified amount of material, and ( 4) on the presence or absence of an attribute in a test result (a go, no-go test). Instructions are also included for methods of test for which precision has not yet been estimated or for which precision and accuracy have been reported in another method of test. For observations based on the measurement of variables, the instructions of this practice specifically apply to test results that are the arithmetic average of individual observations. With qualified assistance, the same general principles can be applied to test results that are based on other functions of the data such as standard deviations.
1.4 This standard includes the following sections: Section No.Attributes, Statements Based on15Binomial Distributions, Calculations for9Binomial Distributions, Statements Based on13Categories of Data7Computer Preparation of Statements Based on Normal or Trans-formed Data12Normal Distributions and Transformed Data, Calculations for8Normal Distributions and Transformed Data, Statements Based on11Poisson Distributions, Calculations for10Poisson Distributions, Statements Based on 14Precision and Bias Based on Other Methods16 Precision Not Established, Statements When17 Ratings, Statements Based on Special Cases of18 Sources of Data6Statistical Data in Two Sections of Methods5Significance and Use4
WITHDRAWN RATIONALE
Formerly under the jurisdiction of Committee D13 on Textiles, this practice was withdrawn in August 2008 in accordance with section 10.5.3.1 of the Regulations Governing ASTM Technical Committees, which requires that standards shall be updated by the end of the eighth year since the last approval date.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D 2906 – 97 (Reapproved 2002)
Standard Practice for
Statements on Precision and Bias for Textiles
This standard is issued under the fixed designation D2906; 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
WorkwasbeguninAugust1966onrecommendationsforstatementsonprecisionandaccuracy.The
firstrecommendationswereissuedasASTMD-13WhitePaper,StatementsonPrecisionandAccuracy,
MARK I, December 1968, prepared by Subcommittee C-6 on Editorial Policy and Review. After a
decision that the recommendations should be a recommended practice under the responsibility of
Subcommittee D13.93, Sampling, Presentation and Interpretation of Data, the recommendations were
revised and published as Practice D2906–70T.
Information was added in Practice D2906–73 on methods (1) for which precision has not been
established, (2) for which test results are not variables, and (3) for which statements are based on
another method. Practice D2906–74 was expanded to include test methods in which test results are
based on the number of successes or failures in a specified number of observations or on the number
ofdefectsorinstancescountedinaspecifiedintervaloftimeorinaspecifiedamountofmaterial.The
present text provides for a nontechnical summary at the beginning of recommended texts based on
normal distributions or on transformed data and for a more positive statement on accuracy when the
true value of a property can be defined only in terms of a test method.
In1984,changeswereintroducedtoreplacetheterm“accuracy”with“bias”asdirectedintheMay
1983 edition of Form and Style for ASTM Standards.
1. Scope the use of components of variance estimated from an analysis
of variance. Instructions covering such calculations are avail-
1.1 Thispracticeservesasaguideforusingtheinformation
able in Practice D2904 or in any standard text (1,2,3,4, and
obtained as directed in Practice D2904 or obtained by other
5).
statistical techniques from other distributions, to prepare state-
1.3 The instructions in this practice are specifically appli-
ments on precision and bias in ASTM methods prepared by
cable to test methods in which test results are based ( 1)onthe
Committee D-13. The manual on form and style for standards
measurement of variables, (2) on the number of successes or
specifies that statements on precision and bias be included in
failures in the specified number of observations, (3)onthe
test methods. Committee D-13 recommends at least a state-
numberofdefectsorincidentscountedinaspecifiedintervalor
ment about single-operator precision in any new test method,
in a specified amount of material, and ( 4) on the presence or
or any test method not containing a precision statement that is
absence of an attribute in a test result (a go, no-go test).
put forward for 5-year approval, in both instances with a
Instructions are also included for methods of test for which
complete statement at the next reapproval. If a provisional test
precisionhasnotyetbeenestimatedorforwhichprecisionand
method is proposed, at least a statement on single-operator
accuracy have been reported in another method of test. For
precision is expected.
observations based on the measurement of variables, the
1.2 The preparation of statements on precision and bias
instructionsofthispracticespecificallyapplytotestresultsthat
requires a general knowledge of statistical principles including
are the arithmetic average of individual observations. With
qualifiedassistance,thesamegeneralprinciplescanbeapplied
ThispracticeisunderthejurisdictionofASTMCommitteeD13onTextilesand
totestresultsthatarebasedonotherfunctionsofthedatasuch
is the direct responsibility of Subcommittee D13.93 on Statistics.
as standard deviations.
Current edition approved Nov. 10, 1997. Published August 1998 . Originally
published as D2906–70 T. Last previous edition D2906–91.
Form and Style for ASTM Standards, May 1983, available from American
Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
19428. this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 2906 – 97 (2002)
1.4 This standard includes the following sections: obtainedfromasinglemethod,forexample,betweenoperators
or between laboratories.
Section No.
3.1.3 characteristic, n—a property of items in a sample or
Attributes, Statements Based on 15
population which, when measured, counted, or otherwise
Binomial Distributions, Calculations for 9
Binomial Distributions, Statements Based on 13 observed, helps to distinguish between the items. (E456)
Categories of Data 7
3.1.4 confidence level, n—the stated proportion of times the
Computer Preparation of Statements Based on Normal or Trans- 12
confidence interval is expected to include the population
formed Data
Normal Distributions and Transformed Data, Calculations for 8
parameter. (E206)
Normal Distributions and Transformed Data, Statements Based on 11
3.1.4.1 Discussion—Statisticians generally accept that, in
Poisson Distributions, Calculations for 10
theabsenceofspecialconsiderations,0.95or95%isarealistic
Poisson Distributions, Statements Based on 14
Precision and Bias Based on Other Methods 16
confidence level. If the consequences of not including the
Precision Not Established, Statements When 17
unknown parameter in the confidence interval would be grave,
Ratings, Statements Based on Special Cases of 18
then a higher confidence level might be considered which
Sources of Data 6
Statistical Data in Two Sections of Methods 5
would lengthen the reported confidence interval. If the conse-
Significance and Use 4
quences of not including the unknown parameter in the
confidenceintervalareoflessthanusualconcern,thenalower
2. Referenced Documents
confidence level might be considered which would shorten the
2.1 ASTM Standards:
reported confidence interval.
D123 Terminology Relating to Textiles
3.1.5 critical difference, n—the observed difference be-
D2904 PracticeforInterlaboratoryTestingofaTextileTest
tweentwotestresultswhichshouldbeconsideredsignificantat
Method that Produces Normally Distributed Data
the specified probability level.
D2905 Practice for Statements on Number of Specimens
4,5 3.1.5.1 Discussion—The critical difference is not equal to
for Textiles
the expected variation in a large number of averages of
E456 Terminology Relating to Quality and Statistics
observed values; it is limited to the expected difference
E691 Practice for Conducting An Interlaboratory Study to
between only two such averages and is based on the standard
Determine the Precision of a Test Method
error for the difference between two averages and not on the
2.2 ASTM Adjuncts:
standard error of single averages.
TEX-PAC
3.1.6 laboratory sample, n—a portion of material taken to
NOTE 1—Tex-Pac is a group of PC programs on floppy disks, available
represent the lot sample, or the original material, and used in
through ASTM Headquarters, 100 Barr Harbor Drive, West Consho-
the laboratory as a source of test specimens.
hocken, PA 19428, USA. The calculations of critical differences and
3.1.7 lot sample, n—one or more shipping units taken at
confidence limits described in the various sections of this practice can be
random to represent an acceptance sampling lot and used as a
performed using some of the programs in this adjunct.
source of laboratory samples.
3. Terminology
3.1.8 parameter, n—in statistics, a variable that describes a
3.1 Definitions: characteristic of a population or mathematical model.
3.1.1 accuracy, n—of a test method, the degree of agree- 3.1.9 percentage point, n—a difference of 1 percent of a
ment between the true value of the property being tested (or
base quantity.
acceptedstandardvalue)andtheaverageofmanyobservations
3.1.9.1 Discussion—Aphrase such as “a difference of X%”
made according to the test method, preferably by many
isambiguouswhenreferringtoadifferenceinpercentages.For
observers. See also bias and precision.
example, a change in the moisture regain of a material from
3.1.1.1 Discussion—Increased accuracy for a test method is
5% to 7% could be reported as an increase of 40% of the
associatedwithdecreasedbiasrelativetoanacceptedreference
initial moisture regain or as an increase of two percentage
value.Although the total bias of a test method is equivalent to
points. The latter wording is recommended.
the accuracy of the test method, the present edition of Form
3.1.10 precision, n—thedegreeofagreementwithinasetof
and Style for ASTM Standards recommends using the term
observations or test results obtained as directed in a method.
“bias” since the accuracy of individual observed values is
3.1.10.1 Discussion—The term “precision”, delimited in
sometimes defined as involving both the precision and the bias
variousways,isusedtodescribedifferentaspectsofprecision.
of the method.
This usage was chosen in preference to the use of “repeatabil-
3.1.2 bias, n—in statistics, a constant or systematic error in
ity” and “reproducibility” which have been assigned conflict-
test results.
ing meanings by various authors and standardizing bodies.
3.1.2.1 Discussion—Bias can exist between the true value
3.1.11 precision, n—under conditions of single-operator
andatestresultobtainedfromonemethod,betweentestresults
precision,thesingle-operator-laboratory-sample-apparatus-day
obtained from two methods, or between two test results
precision of a method; the precision of a set of statistically
independentobservationsallobtainedasdirectedinthemethod
and obtained over the shortest practical time interval in one
Annual Book of ASTM Standards, Vol 07.01.
laboratory by a single operator using one apparatus and
Annual Book of ASTM Standards, Vol 07.02.
randomly drawn specimens from one sample of the material
Annual Book of ASTM Standards, Vol 14.02.
PCprogramsonfloppydisksareavailablethroughASTM.RequestADJD2906. being tested.
D 2906 – 97 (2002)
3.1.11.1 Discussion—Results obtained under conditions of 4.1.5 will be adequate. In all cases, the recommended text in
single-operator precision represent the optimum precision that 4.2 may be part of the statement.
can be expected when using a method. Results obtained under
NOTE 2—The final decision to use a specific method for acceptance
conditions of within-laboratory and between-laboratory preci-
testing of commercial shipments must be made by the purchaser and the
sionrepresenttheexpectedprecisionforsuccessivetestresults
supplier and will depend on considerations other than the precision of the
when a method is used respectively in one laboratory and in
method,includingthecostofsamplingandtestingandthevalueofthelot
more than one laboratory.
of material being tested.
3.1.12 precision, n—under conditions of within-laboratory
4.1.1 If serious disagreements between laboratories is rela-
precision with multiple operators, the multi-operator, single-
tively unlikely, consider the following statement (Note 3).
laboratory-sample, single-apparatus-day (within operator) pre-
cision of a method; the precision of a set of statistically NOTE 3—In these recommended texts, the numbers of sections, notes,
footnotes, equations, and tables are for illustrative purposes and are not
independent test results all obtained in one laboratory using a
intended to conform to the numbers of other parts of this practice. In
single sample of material and with each test result obtained by
correspondence they can be best referenced by such phrases as: “the
a different operator, with each operator using one apparatus to
illustrative text in 4.1.1 numbered as 4.1.2.”
obtain the same number of observations by testing randomly
drawn specimens over the shortest practical time interval. 4.1.2 Method D0000 for the determination of (insert here
3.1.13 precision, n—under conditions of between- the name of the property) is considered satisfactory for
acceptance testing of commercial shipments of (insert here the
laboratory precision, the multi-laboratory, single-sample,
single-operator-apparatus-day (within-laboratory) precision of name of the material) since (insert here the specific reason or
reasons, such as: (1) current estimates of between-laboratory
amethod;theprecisionofasetofstatisticallyindependenttest
results all of which are obtained by testing the same sample of precision are acceptable, (2) the method has been used exten-
sively in the trade for acceptance testing, or ( 3) both of the
materialandeachofwhichisobtainedinadifferentlaboratory
byoneoperatorusingoneapparatustoobtainthesamenumber preceding reasons.)
of observations by testing randomly drawn specimens over the
4.1.3 If it is relatively likely that serious disagreements
shortest practical time interval.
between laboratories may occur but the method is the best
3.1.14 probability level, n—a general term that reflects the
available, consider the following statement (Note 3).
statedproportionoftimesaneventislikelytooccur.(Compare
4.1.4 Method D0000 for the determination of (insert here
to confidence level and significance level.)
the name of the property) may be used for the acceptance
3.1.15 sample, n—(1) a portion of material which is taken
testingofcommercialshipmentsof(insertherethenameofthe
fortestingorforrecordpurposes.(Seealso sample lot; sample,
material) but caution is advised since (insert here the specific
laboratory; and specimen.)(2) a group of specimens used, or
reason or reasons, such as: (1) information on between-
of observations made, which provide information that can be
laboratory precision is lacking or incomplete or (2) between-
used for making statistical inferences about the population(s)
laboratoryprecisionisknowntobepoor.)Comparativetestsas
from which the specimens are drawn.
directed in 4.2.1 may be desirable.
3.1.16 significance level, (a), n—the stated upper limit for
4.1.5 Ifamethodisnotrecommendedforacceptancetesting
the probability of a decision being made that an hypothesis
because a more appropriate method is available, because the
about the value of a parameter is false when in fact it is true.
test is intended for development work only, or because expe-
3.1.17 specimen, n—a specific portion of a material or a
rience has shown that results in one laboratory cannot usually
laboratory sample upon which a test is performed or which is
be verified in another laboratory, consider the following
selected for that purpose. (Syn. test specimen.)
statement
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