ASTM_F_1082_-_00.pdf

Designation:F 1082 00(Reapproved 2000)Standard Practice forTiresDetermining Precision for Test Method Standards1This standard is issued under the fixed designation F 1082;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.INTRODUCTIONKnowing the precision(and where possible the bias and accuracy,or both)of test measurements isvital for efficient technical decision making in any area of technology.For many years the chemicaland allied material industries have addressed the issue of test precision,especially as it applies tointer-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 whenobjects such as tires are tested,especially when tested for various performance features at provinggrounds 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 uniquecharacteristics of some tire tests are kept in mind.This practice gives broad guidelines for tire testprecision 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 thispractice.1.Scope1.1 This practice presents guidelines for preparing clear andmeaningful precision statements for test method standards ontires and related objects pertinent to the tire industry and withinthe scope of ASTM Committee F-9.It gives definitions,explains the potential use of precision for standard test methodsand gives the requirements for interlaboratory or inter-test-siteprograms.The calculation algorithms for determining preci-sion and the format for expressing precision are also given.2.Referenced Documents2.1 ASTM Standards:E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2F 538 Terminology Relating to the Characteristics and Per-formance of Tires33.Terminology3.1 Definitions of Terms3.1.1 accuracy,na measurement concept that describesthe degree of correspondence between an average measuredvalue and an accepted reference or standard value for theobject,material or phenomenon under test.3.1.1.1 DiscussionThe reference value may be estab-lished by theory,by reference to an accepted standard,toanother test method,or in some cases the average that could beobtained by applying the test method to all of the samplingunits comprising a lot.3.1.2 bias,nthe difference between the average measuredtest result and the accepted reference value;it measures in aninverse manner the accuracy of a test.3.1.2.1 DiscussionAlarge bias implies poor accuracy,anda small or negligible bias denotes a high accuracy;when biasexists,increased testing does not increase accuracy,but merelygives an increased confidence in the bias estimate.3.1.3 determination,nthe application of the completemeasurement procedure to one piece,specimen or object toproduce one numerical measured value to be used to form anaverage or median.3.1.4 precision,na measurement concept that expressesthe ability to generate test results that agree with each other inabsolute magnitude.3.1.4.1 DiscussionThe degree of agreement is normallymeasured inversely by the standard deviation,high precisioncorresponds to a low(small)standard deviation.High precisionmay exist simultaneously with a large bias or poor accuracy.3.1.5 repeatability,r,nan established value,below which1This practice is under the jurisdiction of ASTM Committee F09 on Tires and isthe direct responsibility of Subcommittee F09.10 on Equipment,Facilities,andCalibration.Current edition approved May 10,2000.Published July 2000.Originallypublished as F 1082 87.Last previous edition F 1082 93.2Annual Book of ASTM Standards,Vol 14.02.3Annual Book of ASTM Standards,Vol 09.02.1Copyright ASTM,100 Barr Harbor Drive,West Conshohocken,PA 19428-2959,United States.the absolute difference between two“within-laboratory”or“within test-site”test results may be expected to lie,with aspecified probability.3.1.5.1 DiscussionThe two test results are obtained withthe same method on nominally identical test materials underthe same conditions(same operator,apparatus,laboratory,location,and specified time period),and in the absence of otherindications,the specified probability is 0.95(sometimes writtenas 95%).The“established value”also may be called a“criticaldifference.”3.1.6 repeatability,relative(r),na repeatability estimateexpressed as a percentage of the average of the property forwhich the estimate was obtained.3.1.6.1 DiscussionIt is often appropriate to