CLSI EP15-A3:verification of precision and estimation of bias
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We are plead to have a guest essay explaining the latest in Method Verification,specifically the newest version of the CLSI guideline EP15on Method Verification.For labs eking a qui ck check to insure their methods are meeting manufacturer specifications,EP15may be the r ight choice
What's New in CLSI EP15-A3:Ur Verification of Precision and Estimation of Bias;Ap proved Guideline-Third Edition R.Neill Carey,Ph.D.July2015纳尼亚传奇2 凯斯宾王子
Introduction
sceoCLSI EP15was relead as an A3document in September2014.This is its fourth iteration,and alt hough it retains much of its original approach,there were some significant changes in the A3vers ion.
The most significant change is the creation of a relatively simple experiment that gives reliable es timates of a measurement procedure's imprecision and its bias.The esntials to accomplish this were prent in EP15through all of its previous versions,but they are refined and combined in EP 15-A3to make a single experiment.Here's a brief description of the protocol.
Specification of Acceptable Performance
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Before doing anything el,the ur should specify total allowable error,and derive from it the all owable standard deviation(or%CV),and the allowable bias.The ur should ascertain that the i mprecision of the candidate measurement procedure meets the criterion for allowable imprecisi on before beginning the evaluation.If the measurement procedure's imprecision reported in publ ications,such as the manufacturer's stated imprecision,does not meet the criterion,the precisio n verification procedure described in EP15-A3is not appropriate.Being a limited experiment,it is less rigorous than the experiment described in CLSI EP5-A3,which would be mor e appropriate.
Verification of Precision
EP15first describes a precision verification experiment.If the ur is evaluating a procedure for w hich there are manufacturer's precision claims,or published precision results,that were develope
d using CLSI EP5,th
e ur can verify the published precision in an experiment lasting as few as fiv
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e days.
Patient samples,reference materials,proficiency testing samples,or control materials may be u d a
s the test samples,provided there is sufficient sample material for testing each sample five tim es per run for five to ven runs.Precision should be tested with two or more sample materials at different medical decision point
concentrations.The experiment produces at least25replicates collected over at least5days for e ach sample material.
The repeatability(previously termed"within-run")and the within-laboratory(previously termed "total")standard deviations are calculated by an analysis of variance technique(ANOVA)that pro perly accounts for the within-run and
between-run contributions to the overall imprecision of the measurement procedure.The ur n eeds access to software to do the ANOVA calculations,but they are
available in Excel,Minitab,Analyze-it,and other software packages that do statistical calculations. The repeatability and within-laboratory standard deviations are then compared to the claimed or published standard deviations.If the calculated standard deviations are less than the published v alues,the ur has verified the claim.Sometimes the calculated standard deviations may exceed t he published values,and yet the true standard deviations are less than the published values.For exampl
e,if the true standard deviations were actually exactly equal to their claimed counterparts, the calculated standard deviations would exceed their published counterparts fifty percent of th e time in verification experiments.To allow for this possibility,the ur calculates a"verification li mit"bad on the published standard deviation and the size of the ur's experiment.If the calcu lated standard deviation is less than the verification limit,it is not statistically significantly larger t han the published standard deviation,and the ur has verified the published precision.If the cal culated precision exceeds the verification limit,the calculated standard deviation is statistically si gnificantly larger than the published standard deviation,and the ur has failed to verify the publ ished imprecision.The document includes tables to simplify the calculation of the verification limi t.
乔丹名人堂演讲Estimation of Bias
Becau the precision experiment has so many replicate measurements,collected over veral da ys,results from the precision experiment may be ud to make a reliable estimate of the bias of t he measurement procedure relative to the assigned(target)values of the sample materials ud i n the experiment.The only requirement is that the assigned value must be available.The choice of material depends on the purpo of the ur in estimating the bias.Two or more appropriate materials should be tested in the precision experiment.considerably
If the ur is interested in estimating bias relative to the peer group for proficiency testing,and w ants to estimate how the measurement procedure will perform well on proficiency testing,profici ency testing materials with peer group values for the measurement procedure being evaluated ar e appropriate.新版中日交流标准日本语
中英翻译网站For bias relative to the quality control peer group,quality control materials with peer group value s for the measurement procedure are appropriate."Assayed"quality control materials are not ap propriate,unless peer group information is available.Typically,there is no way to estimate the un certainty of the"assayed"values,which is needed to determine if the calculated bias is statisticall y significant.
Internationally recognized high order reference materials,such as a material from the U.S.Nation al Institute of Standards and Technology,or from the Joint Committee for Traceability in Laborato ry Medicine,or from similar organizations may be appropriate if the ur wishes to estimate the bias relative to the assigned
concentrations of such materials.U of the materials is important in establishing the traceabili ty of measurement procedures.
Patient samples or control materials which have been repeatedly assayed with a measurement pr ocedure felt to be substantially equivalent to the measurement
procedure being evaluated may be appropriate if the ur is interested in estimating bias relative顺利英文
to that measurement procedure.This could be uful,for example,if the intent of the experimen t was to estimate the bias of one laboratory in a system relative to another,or to the mean of the laboratories in a system.
If the sample materials are appropriate,and target concentrations are available,the ur can esti mate the bias between the mean concentration calculated in the precision experiment relative to the target concentration of each of the materials.
To determine whether there is any statistically significant bias between the mean concentration c alculated from the experiment and the target concentration,the ur calculates a“verification int erval”around the target concentration.The width of the verification interval depends on the unc ertainty of the target value of the reference material and the standard error of the calculated me an concentration from the experiment.Calculation of the verification interval would be complicat ed,but the committee simplified it greatly by providing tables for the difficult-to-calculate quantities bad on
the number of replicate measurements per run,the number of runs,and the uncertainty of the target value.
If the mean concentration from the ur's experiment is within the verification interval,there is n o statistically significant bias.
