1、Designation: E 2554 07Standard Practice forEstimating and Monitoring the Uncertainty of Test Resultsof a Test Method in a Single Laboratory Using a ControlSample Program1This standard is issued under the fixed designation E 2554; the number immediately following the designation indicates the year of
2、original 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.1. Scope1.1 This practice describes techniques for a laboratory toesti
3、mate the uncertainty of a test result using data from testresults on a control sample.1.2 Uncertainty as defined by this practice applies to thecapabilities of a single laboratory. Any estimate of uncertaintydetermined through the use of this practice applies only to theindividual laboratory for whi
4、ch the data are presented.1.3 The laboratory uses a well defined and established testmethod in determining a series of test results. The uncertaintyestimated using this practice only applies when the same testmethod is followed. The uncertainty only applies for thematerial types represented by the c
5、ontrol samples, and multiplecontrol samples may be needed, especially if the method hasdifferent precision for different sample types or response levels.1.4 The uncertainty estimate determined by this practicerepresents the intermediate precision of test results. Thisestimate seeks to quantify the t
6、otal variation expected within asingle laboratory using a single established test method whileincorporating as many known sources of variation as possible.1.5 This practice does not establish error estimates (errorbudget) attributed to individual factors that could influenceuncertainty.1.6 This prac
7、tice describes the use of control charts toevaluate the data obtained and presents a special type of controlchart to monitor the estimate of uncertainty.1.7 The system of units for this Standard is not specified.Dimensional quantities in the Standard are presented only asillustrations of calculation
8、 methods. The examples are notbinding on products or test methods treated.1.8 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
9、 the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 5184 Test Methods for Determination of Aluminum andSilicon in Fuel Oils by Ashing, Fusion, InductivelyCoupled Plasma Atomic Emission Spectrometry, andAtomic Absorption SpectrometryE 177 Practice f
10、or Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 1707 Guide for Estimating Uncertainties in Dosimetry forRadiation Processing3E 2282 Guide for Defining the Test Result of a Test Method2.2 ASTM Publication:Manual on Presentation of Data a
11、nd Control ChartAnalysis, 7th Edition22.3 ISO Standard:ISO 17025 General Requirements for the Competence ofTesting and Calibration Laboratories43. Terminology3.1 DefinitionsThe terminology of Terminology E 456applies to this practice except as modified herein.3.1.1 control sample, nsample taken from
12、 a stable, homo-geneous material for the purposes of monitoring the perfor-mance of a test method in a laboratory.3.1.1.1 DiscussionThe control sample material is repre-sentative of the product typically tested in the laboratory by thegiven test method. A control sample is run periodically usingthe
13、complete test method protocol to develop a test result. Such1This practice is under the jurisdiction of ASTM Committee E11 on Quality andStatistics and is the direct responsibility of Subcommittee E11.20 on Test MethodEvaluation and Quality Control.Current edition approved May 1, 2007. Published Jun
14、e 2007.2For 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.3Withdrawn.4Available from American National Standards
15、 Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.test results may be statistically evaluated to monitor testmethod performance over time. It is not ne
16、cessary to have anaccepted reference value assigned to the control sample mate-rial. When the current material is nearly consumed, a replace-ment material should be run in parallel with the currentmaterial to ensure continuity in the control sample program.3.1.2 check sample, nsee control sample.3.1
17、.3 uncertainty control chart, ncontrol chart that in-cludes control limits based on the variation attributed to theuncertainty of the test method.3.1.4 intermediate precision, nthe closeness of agreementbetween test results obtained under specified intermediateprecision conditions. E 1773.1.4.1 Disc
18、ussionThe specific measure and the specificconditions must be specified for each intermediate measure ofprecision; thus, “standard deviation of test results amongoperators in a laboratory,” or “day-to-day standard deviationwithin a laboratory for the same operator.”3.1.4.2 DiscussionBecause the trai
19、ning of operators, theagreement of different pieces of equipment in the samelaboratory and the variation of environmental conditions withlonger time intervals all depend on the degree of within-laboratory control, the intermediate measures of precision arelikely to vary appreciably from laboratory t
20、o laboratory. Thus,intermediate precisions may be more characteristic of indi-vidual laboratories than of the test method.3.1.5 test result, nthe value of a characteristic obtained bycarrying out a specified test method. E 22823.1.6 repeatability, nprecision under repeatability condi-tions. E 1774.
21、Summary of Practice4.1 A standard material or control sample is measuredrepeatedly over time. The presumption of this practice is thatthe variation experienced on this material will be indicative ofthe laboratory total expected variation. Incorporation of spe-cific known or potential sources of vari
22、ation in the testingprogram is encouraged.4.2 A control chart is prepared and the results are evaluatedto identify short-term variation and longer-term variation.These data can then be used to determine an estimate ofuncertainty standard deviation.4.3 Laboratories already having control chart proced
23、ures inplace may use existing data.4.4 Ongoing monitoring of the test method is conductedusing an uncertainty control chart.5. Significance and Use5.1 Laboratories accredited under ISO 17025 are required topresent uncertainty estimates for their test results. This practiceprovides procedures that us
24、e test results to develop uncertaintyestimates for an individual laboratory.5.2 Generally, these test results will be from a single sampleof stable and homogeneous material known as a control orcheck sample.5.3 The true value of the characteristic(s) of the controlsample being measured will ordinari
25、ly be unknown. However,this methodology may also be used if the control sample is areference material, in which case the test method bias may alsobe estimated and incorporated into the uncertainty estimate.Many test methods do not have true reference materialsavailable to provide traceable chains of
26、 uncertainty estimation.5.4 This practice also allows for ongoing monitoring of thelaboratory uncertainty. As estimates of the level of uncertaintychange, possibly as contributions to uncertainty are identifiedand minimized, revision to the laboratory uncertainty will bepossible.6. General Considera
27、tions6.1 Materials to be Used:6.1.1 This methodology requires a quantity of stable andhomogeneous material which will serve as the source ofcontrol samples (sometimes called check samples). The mate-rial shall be similar in composition to the samples of materialroutinely analyzed by this test method
28、 in this laboratory. Bystable it is assumed that the test results obtained from thismaterial should be consistent over the time interval that thismaterial will be used. By homogeneous it is assumed thatsamples taken from the material source will not have asignificant variation in the characteristic
29、measured by the testmethod.6.1.2 For destructive testing of control sample materials,provision shall be made for depletion and replacement of thecontrol sample material.6.1.2.1 In some cases, the test method may be nondestruc-tive and the same material may be reused indefinitely.6.1.2.2 In other cas
30、es, the material may be used up, dete-riorate, or otherwise gradually change.6.1.3 The test method should describe the best practices forpreparing and storing the control material and taking thecontrol samples.6.2 Test Conditions:6.2.1 An uncertainty estimation program should be de-signed to include
31、 all known sources of variation, such asoperators (analysts), equipment, reagents, and so forth, andthese should be deliberately incorporated into the design of theprogram. In general, these sources of variation will be defined(including acceptable tolerances) by the test method.6.2.2 In cases in wh
32、ich control over such variations is notpossible or undefined, at least 30 to 50 sampling periods shallbe evaluated to permit environmental and other factors to beincorporated in the overall estimate.7. Overall ProcedureControl Charting Methods7.1 General concepts of control charts are described else
33、-where, such as in Manual 7A.57.2 The general procedure involves two major phases:Preliminary and Monitoring.7.2.1 Preliminary Phase:7.2.1.1 This phase begins with an initial collection of testresults.7.2.1.2 Preliminary control charts are then prepared andexamined. These charts are evaluated to det
34、ermine if theprocess is in a state of statistical control. The usual principles5Manual on Presentation of Data and Control Chart Analysis: 7th Edition ,ASTM International, West Conshohocken, PA, 2001.E2554072of control charting utilize short-term variability to estimate thelimits within which sample
35、s of test results should vary. Forcontrol sample programs this short-term variability is equiva-lent to repeatability precision. It is expected, however, thatadditional contributions to variation will be present over timeand therefore additional variation, equivalent to intermediateprecision, will b
36、e encountered.7.2.1.3 An estimate of uncertainty standard deviation isdeveloped.7.2.1.4 An uncertainty control chart is then prepared tomonitor future sample results.7.2.2 Monitoring Phase:7.2.2.1 The proposed uncertainty control chart is used toprovide evidence that the estimate of uncertainty is n
37、otexceeding the estimated value.7.2.2.2 The estimate of uncertainty should be periodicallyre-evaluated.7.2.2.3 Where appropriate, it is recommended that a stan-dard control chart also be maintained to determine whether thevariation over time has been reduced to the level of short-termvariation (repe
38、atability).7.3 Two types of control charting methods are recom-mended to develop estimates of uncertainty. These include:7.3.1 Mean (Xbar) and range or standard deviation chartsare used when multiple test results are conducted in each timeperiod.7.3.2 Individual charts (IndX) are used when single te
39、stresults are obtained in each time period.7.4 Variation Estimates:7.4.1 Either a range chart or a standard deviation chart maybe used to estimate the short-term variability when multipleassays are conducted under repeatability conditions per timeperiod. An estimate from the control chart data can b
40、ecompared to other estimates of repeatability (within laboratory,short-term variation) if available.7.4.2 Sample averages are examined and may provideestimates of variation caused by other factors. Such factorsmay include environmental effects, operator factors, reagents,or instruments.7.5 Systemati
41、c Procedures:7.5.1 Specifically designed experiments can be used toensure all known sources of variation, such as operators(analysts), equipment, reagents, or instruments are incorpo-rated in the general study.7.5.2 The data generated from this program is available foradditional uses, such as contro
42、l charting to evaluate trends,stratification by analysis, or stratification by equipment toidentify training or maintenance needs or both.8. Specific Procedures8.1 Multiple Test Results Generated per Time Period:8.1.1 A specified number of independent test results aretaken during each time period. G
43、enerally this number is 5 orless. It is preferred that at least 25 sets of test results beobtained before developing the charts.8.1.2 Either a range chart or a standard deviation chart isprepared. This is examined for special cause variation. If thevariability appears random then an estimate of repe
44、atability iscomputed. This may be done by pooling the sums of squares,using the average standard deviation, or using the averagerange.NOTE 1If the ranges or standard deviations are zero in most of thesamples, then this estimate of repeatability standard deviation is suspectand probably unusable. Thi
45、s is usually the result of insufficient resolutionof the measurement system in use or severe rounding. An estimate basedon the minimum interval size should be substituted for the zeros.As a ruleof thumb, consider replacing the zeros when more than about13 are zeros.8.1.3 A means chart is used to exa
46、mine variation amongtime periods. Limits on this chart permit comparison ofvariation between time periods using repeatability as theestimate of error.8.1.3.1 If the control chart shows a state of statistical controlthen the uncertainty will be assumed approximately equivalentto the repeatability sta
47、ndard deviation.8.1.3.2 In most cases it will be expected that the variabilitybetween means will show an “out of control” conditionindicating that there are “special” causes of variation inaddition to repeatability. The between means variation andwithin means repeatability estimates are then used to
48、 computean estimate of uncertainty standard deviation.8.1.4 Using the estimate of uncertainty standard deviationan Uncertainty Control Chart is prepared for future monitoringof the uncertainty. This chart may include control limits formeans as a possible lower set of control limits along with theunc
49、ertainty control limits based on the estimate of uncertainty.8.2 Individual Tests:8.2.1 Single tests are generated at each time period. Varia-tion among these results is evaluated.8.2.2 In some cases, it is possible to incorporate externalestimates of repeatability obtained from prior or concurrentstudies.9. Multiple Readings per Time Period9.1 Example 1Absorbance of Radiochromic Dosimeters:9.1.1 Over a period of several days, different sets of threedosimeters were irradiated to the same nominal dose. Theirradiation was conducted under standard conditions at a singleirrad
