ASTM_D_7366_-_08_2013.pdf

Designation:D736608(Reapproved 2013)Standard Practice forEstimation of Measurement Uncertainty for Data fromRegression-based Methods1This standard is issued under the fixed designation D7366;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.1.Scope1.1 This practice establishes a standard for computing themeasurement uncertainty for applicable test methods in Com-mittee D19 on Water.The practice does not provide a single-point estimate for the entire working range,but rather relatesthe uncertainty to concentration.The statistical technique ofregression is employed during data analysis.1.2 Applicable test methods are those whose results comefrom regression-based methods and whose data are intra-laboratory(not inter-laboratory data,such as result fromround-robin studies).For each analysis conducted using such amethod,it is assumed that a fixed,reproducible amount ofsample is introduced.1.3 Calculation of the measurement uncertainty involves theanalysis of data collected to help characterize the analyticalmethod over an appropriate concentration range.Examplesources of data include:1)calibration studies(which may ormay not be conducted in pure solvent),2)recovery studies(which typically are conducted in matrix and include allsample-preparation steps),and 3)collections of data obtainedas part of the methods ongoing Quality Control program.Useof multiple instruments,multiple operators,or both,andfield-sampling protocols may or may not be reflected in thedata.1.4 In any designed study whose data are to be used tocalculate method uncertainty,the user should think carefullyabout what the study is trying to accomplish and muchvariation should be incorporated into the study.General guid-ance on designing studies(for example,calibration,recovery)is given in Appendix A.Detailed guidelines on sources ofvariation are outside the scope of this practice,but generalpoints to consider are included in Appendix B,which is notintended to be exhaustive.With any study,the user must thinkcarefully about the factors involved with conducting theanalysis,and must realize that the computed measurementuncertainty will reflect the quality of the input data.1.5 Associated with the measurement uncertainty is a user-chosen level of statistical confidence.1.6 At any concentration in the working range,the measure-ment uncertainty is plus-or-minus the half-width of the predic-tion interval associated with the regression line.1.7 It is assumed that the user has access to a statisticalsoftware package for performing regression.A statisticianshould be consulted if assistance is needed in selecting such aprogram.1.8 A statistician also should be consulted if data transfor-mations are being considered.1.9 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to Water3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 confidence levelthe probability that the predictioninterval from a regression estimate will encompass the truevalue of the amount or concentration of the analyte in asubsequent measurement.Typical choices for the confidencelevel are 99%and 95%.3.1.2 fitting techniquea method for estimating the param-eters of a mathematical model.For example,ordinary leastsquares is a fitting technique that may be used to estimate theparameters a0,a1,a2,of the polynomial model y=a0+a1x+a2x2+,based on observed x,y pairs.Weighted leastsquares is also a fitting technique.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 Jan.1,2013.Published January 2013.Originallyapproved in 2008.Last previous approval in 2008 as D7366 08.DOI:10.1520/D7366-08R13.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.3 lack-of-fit(LOF)testa statistical technique whenreplicate data are available;computes the significance ofresidual means to replicate y variability,to indicate whetherdeviations from model predictions are reasonably accountedfor by random variability,thus indicating that the model isadequate;at each concentration,compares the amount ofresidual variation from model prediction with th