ASTM_C_1215_-_92_2012e1.pdf

Designation:C121592(Reapproved 2012)1Standard Guide forPreparing and Interpreting Precision and Bias Statements inTest Method Standards Used in the Nuclear Industry1This standard is issued under the fixed designation C1215;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()indicates an editorial change since the last revision or reapproval.1NOTEChanges were made editorially in June 2012.INTRODUCTIONTest method standards are required to contain precision and bias statements.This guide contains aglossary that explains various terms that often appear in these statements as well as an exampleillustrating such statements for a specific set of data.Precision and bias statements are shown to varyaccording to the conditions under which the data were collected.This guide emphasizes that the errormodel(an algebraic expression that describes how the various sources of variation affect themeasurement)is an important consideration in the formation of precision and bias statements.1.Scope1.1 This guide covers terminology useful for the preparationand interpretation of precision and bias statements.This guidedoes not recommend a specific error model or statisticalmethod.It provides awareness of terminology and approachesand options to use for precision and bias statements.1.2 In formulating precision and bias statements,it isimportant to understand the statistical concepts involved and toidentify the major sources of variation that affect results.Appendix X1 provides a brief summary of these concepts.1.3 To illustrate the statistical concepts and to demonstratesome sources of variation,a hypothetical data set has beenanalyzed in Appendix X2.Reference to this example is madethroughout this guide.1.4 It is difficult and at times impossible to ship nuclearmaterials for interlaboratory testing.Thus,precision statementsfor test methods relating to nuclear materials will ordinarilyreflect only within-laboratory variation.1.5 No units are used in this statistical analysis.1.6 This guide does not involve the use of materials,operations,or equipment and does not address any riskassociated.2.Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ANSI Standard:ANSI N15.5 Statistical Terminology and Notation forNuclear Materials Management33.Terminology for Precision and Bias Statements3.1 Definitions:3.1.1 accuracy(seebias)(1)bias.(2)the closeness of ameasured value to the true value.(3)the closeness of ameasured value to an accepted reference or standard value.3.1.1.1 DiscussionFor many investigators,accuracy isattained only if a procedure is both precise and unbiased(seebias).Because this blending of precision into accuracy canresult occasionally in incorrect analyses and unclear statementsof results,ASTM requires statement on bias instead of accu-racy.43.1.2 analysis of variance(ANOVA)the body of statisticaltheory,methods,and practices in which the variation in a set ofdata is partitioned into identifiable sources of variation.1This guide is under the jurisdiction of ASTM Committee C26 on Nuclear FuelCycle and is the direct responsibility of Subcommittee C26.08 on QualityAssurance,Statistical Applications,and Reference Materials.Current edition approved June 1,2012.Published June 2012.Originallyapproved in 1992.Last previous edition approved in 2006 as C121592(2006).DOI:10.1520/C1215-92R12E01.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute(ANSI),25 W.43rd St.,4th Floor,New York,NY 10036,http:/www.ansi.org.4Refer to Form and Style for ASTM Standards,8th Ed.,1989,ASTM.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 Sources of variation may include analysts,instruments,samples,and laboratories.To use the analysis of variance,thedata collection method must be carefully designed based on amodel that includes all the sources of variation of interest.(SeeExample,X2.1.1)3.1.3 bias(see accuracy)a constant positive or negativedeviation of the method average from the correct value oraccepted reference value.3.1.3.1 DiscussionBias represents a constant error as op-posed to a random error.(a)A method bias can be estimated by the difference(orrelative difference)between a measured average and an ac-cepted standard or reference value.The data from which theestimate is obtained should be statistically analyzed to establishbias in the presence of random error.A thorough bias investi-gation of a measurement procedure requires