ASTM_D_2905_-_97_2002.pdf

Designation:D 2905 97(Reapproved 2002)Standard Practice forStatements on Number of Specimens for Textiles1This standard is issued under the fixed designation D 2905;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice provides a mechanism for calculating thenumber of specimens per laboratory sampling unit.It alsoprovides recommended texts to be used in exceptional cases.Ordinarily,it is preferable to specify in the section on samplinga small fixed number of specimens for each laboratory sam-pling unit.Occasionally,however,the task group writing a testmethod may think that the variability among the observationson specimens within a laboratory sampling unit will probablydiffer significantly from laboratory to laboratory.It is inunusual cases of this sort that the recommended texts in thispractice should be used.1.1.1 Paragraph A14.8 of the Recommendations on Formand Style specifies that statements on the number of specimensbe included in all test methods.1.2 This practice covers six optional recommended textswhich serve as guides for the preparation of statements on thenumber of specimens required to determine the average qualityof each unit of the laboratory sample under various conditions.The choice of the text to be used in a specific method willdepend on the purpose of the test and the available information.This practice covers the following six different conditions.Recom-mendedTextConditionsSections1Standard Deviation with Two-sided Limits10,112Standard Deviation with One-sided Limits13,143Coefficient of Variation with Two-sided Limits16,174Coefficient of Variation with One-sided Limits19,205Variability Known,Fixed Number of Specimens226Variability Not Known,Fixed Number of Speci-mens241.3 Recommended Texts 1 through 4 are preceded byexamples.Each example states part of the data from aninterlaboratory test and illustrates the decisions needed in thecourse of calculating the numerical values required for inclu-sion in a specific text.Each of these texts describes twoconditions:(1)the procedure to be followed when the user hasa reliable estimate of the variability of the method in his ownlaboratory,and(2)the fixed number of specimens requiredwhen the user does not have a reliable estimate of thevariability of the method in his own laboratory.1.4 The instructions in this practice are specifically appli-cable to methods based on the measurement of variates.Theinstructions are not generally applicable to data based onattributes,and as a result,are not usually used for methodsbased on“go,no-go”tests.1.5 This practice does not specify or discuss sampling plansbut assumes that sampling has been adequately covered inother sections of the test method under preparation.However,to obtain the total number of specimens on which to base adecision to accept or reject a lot when acceptance testing acommercial shipment,multiply the number of specimens foreach unit or the laboratory sample by the total number of suchunits in the entire lot sample.Instructions on the number ofunits in the laboratory sample to be taken from each of theprimary sampling units in the lot sample should be in theapplicable material specification or other agreement betweenthe purchaser and the supplier.2.Referenced Documents2.1 ASTM Standards:D 123 Terminology Relating to Textiles2D 2904 Practice for Interlaboratory Testing of a Textile TestMethod that Produces Normally Distributed Data2D 2906 Practice for Statements on Precision and Bias forTextiles2D 4271 Practice for Writing Statements on Sampling in TestMethods for Textiles3E 122 Practice for Choice of Sample Size to Estimate aMeasure of Quality for a Lot or Process4E 456 Terminology Relating to Quality and Statistics4E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method42.2 ASTM Adjuncts:TEX-PAC5NOTE1Tex-Pac is a group of PC programs on floppy disks,available1This practice is under the jurisdiction of ASTM Committee D13 on Textiles,and is the direct responsibility of Subcommittee D13.93 on Statistics.Current edition approved Sept.10,1997.Published August 1998.Originallypublished as D 2905 71 T.Last previous edition D 2905 91.2Annual Book of ASTM Standards,Vol 07.01.3Annual Book of ASTM Standards,Vol 07.02.4Annual Book of ASTM Standards,Vol 14.02.5PC programs on floppy disks are available throughASTM.RequestADJD2904.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.through ASTM Headquarters,100 Barr Harbor Drive,West Consho-hocken,PA 19428,USA.The calculations for the numbers of specimensdescribed in the various sections of this practice can be performed usingone of the programs in this adjunct.3.Terminology3.1 Definitions:3.1.1 a