ASTM_D_7729_-_12_2018e1.pdf

Designation:D772912(Reapproved 2018)1Standard Practice forDetermining and Expressing Precision of MeasurementResults,in the Analysis of Water,as Relative StandardDeviation,Utilizing DQCALC Software1This standard is issued under the fixed designation D7729;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.1NOTEThe Keywords section was added editorially in August 2018.1.Scope1.1 This practice describes a procedure for developing agraphical model of relative standard deviation versus concen-tration for analytical methods used in the analysis of water(methods that are subject to non-additive random errors)for thepurpose of assigning a statement of noise or randomness toanalytical results(commonly referred to as a precisionstatement),in either a manual or an automated fashion.1.2 Data analysis and modeling is done with CommitteeD19 Adjunct DQCALC2(a Microsoft Excel3-based tool).1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Introduction2.1 An understanding of the uncertainty associated withmeasurement results is necessary for evaluating the utility ofthose results.Without a reported uncertainty estimate,users ofmeasurement results are unable to determine if the data aresufficiently precise for any specific data use.2.2 Measurement uncertainty(MU)is most generally un-derstood to be“a parameter characterizing the dispersion of thequantity values being attributed to a measurand”(from VIM2.26).This definition can be implemented as an expression(“uncertainty statement”)associated with an reported measure-ment that represents the statistically based(Type A estimate)dispersion of experimental results around a reported value.2.3 There is no universally agreed upon format or nomen-clature for uncertainty statements.The literature offers sugges-tions ranging from simple expressions of standard deviation or“fractional uncertainty”(standard deviation divided by re-ported result)to confidence intervals to detailed“uncertaintyreports.”2.4 In addition to the“random”errors encompassed in theideas expressed in 1.1 and 1.2,there are also“systematic”errors,biases,that can be considered as part of uncertainty.Theliterature is not consistent on how unknown bias is consideredin an uncertainty statement.For purposes of this practice,biasis assumed to have been corrected for or insignificant in thereported results,and bias is not specifically incorporated in theproposed uncertainty statement.2.5 For purposes of this practice,the terms MU,uncertaintystatement,or measurement uncertainty will be used synony-mously to designate the expression accompanying measure-ment results for the purpose of assessing the utility of thoseresults.2.6 This practice proposes the use of fractional uncertaintyor relative standard deviation(RSD)as the expression of MU.2.7 Traditionally,in the generation and publication of datarelated to the analysis of water,a continuous function(model)describing the relationship of uncertainty(as standard devia-tion)to concentration is not available.To compensate for thislack,discrete points bounding certain levels of uncertainty arecalculated,for example,“detection limits”(typically around33%RSD)and“quantitation limits”(often around 10%1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.02 on Quality Systems,Specification,and Statistics.Current edition approved Aug.1,2018.Published September 2018.Originallyapproved in 2012.Last previous edition approved in 2012 as D7729 12.DOI:10.1520/D7729-12R18E01.2Available fromASTM International Headquarters.OrderAdjunct No.ADJDQ-CALC.Original adjunct produced in 2007.3Microsoft Excel is a trademark of the Microsoft Corporation,Redmond,WA.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trad