1、Designation: E2554 07E2554 13 An American National StandardStandard Practice forEstimating and Monitoring the Uncertainty of Test Resultsof a Test Method in a Single Laboratory Using a ControlSample ProgramUsing Control Chart Techniques1This standard is issued under the fixed designation E2554; the
2、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. Sc
3、ope1.1 This practice describes techniques for a laboratory to estimate the uncertainty of a test result using data from test results ona control sample. This standard provides one method for a laboratory to estimate Measurement Uncertainty in accordance withSection A22.3 in Form and Style of ASTM St
4、andards.1.2 Uncertainty as defined by this practice applies to the capabilities of a single laboratory. Any estimate of uncertaintydetermined through the use of this practice applies only to the individual laboratory for which the data are presented.1.3 The laboratory uses a well defined and establi
5、shed test method in determining a series of test results. The uncertaintyestimated using this practice only applies when the same test method is followed. The uncertainty only applies for the materialtypes represented by the control samples, and multiple control samples may be needed, especially if
6、the method has differentprecision for different sample types or response levels.1.4 The uncertainty estimate determined by this practice represents the intermediate precision of test results. This estimate seeksto quantify the total variation expected within a single laboratory using a single establ
7、ished test method while incorporating asmany known sources of variation as possible.1.5 This practice does not establish error estimates (error budget) attributed to individual factors that could influenceuncertainty.1.6 This practice describes the use of control charts to evaluate the data obtained
8、 and presents a special type of control chartto monitor the estimate of uncertainty.1.7 The system of units for this Standardstandard is not specified. Dimensional quantities in the Standardstandard are presentedonly as illustrations of calculation methods. The examples are not binding on products o
9、r test methods treated.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior t
10、o use.2. Referenced Documents2.1 ASTM Standards:2D5184 Test Methods for Determination of Aluminum and Silicon in Fuel Oils by Ashing, Fusion, Inductively Coupled PlasmaAtomic Emission Spectrometry, and Atomic Absorption SpectrometryE177 Practice for Use of the Terms Precision and Bias in ASTM Test M
11、ethodsE456 Terminology Relating to Quality and Statistics51707 Guide for Estimating Uncertainties in Dosimetry for Radiation ProcessingE2282 Guide for Defining the Test Result of a Test MethodE2587 Practice for Use of Control Charts in Statistical Process ControlISO/ASTM 51707 Guide for Estimating U
12、ncertainties in Dosimetry for Radiation Processing1 This practice is under the jurisdiction of ASTM Committee E11 on Quality and Statistics and is the direct responsibility of Subcommittee E11.20 on Test MethodEvaluation and Quality Control.Current edition approved May 1, 2007April 1, 2013. Publishe
13、d June 2007May 2013. Originally approved in 2007. Last previous edition approved in 2007 as E2554 07. DOI: 10.1520/E2554-07.10.1520/E2554-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolum
14、e information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequa
15、tely depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
16、n, PA 19428-2959. United States12.2 ASTM Publication:Publications:2Form and Style for ASTM StandardsManual on Presentation of Data and Control Chart Analysis,Analysis 7th Edition2.3 ISO Standard:3ISOISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories3. Termi
17、nology3.1 Definitions:Definitions3.1.1 The terminology of Terminology E456 applies to this practice except as modified herein.The terminology ofTerminology E456 applies to this practice except as modified herein.3.1.1 control sample, nsample taken from a stable, homogeneous material for the purposes
18、 of monitoring the performance ofa test method in a laboratory.3.1.1.1 DiscussionThe control sample material is representative of the product typically tested in the laboratory by the given test method. A controlsample is run periodically using the complete test method protocol to develop a test res
19、ult. Such test results may be statisticallyevaluated to monitor test method performance over time. It is not necessary to have an accepted reference value assigned to thecontrol sample material. When the current material is nearly consumed, a replacement material should be run in parallel with thecu
20、rrent material to ensure continuity in the control sample program.3.1.2 check sample, nsee control sample.3.1.4 uncertainty control chart, ncontrol chart that includes control limits based on the variation attributed to the uncertaintyof the test method.3.1.3 intermediate precision, nthe closeness o
21、f agreement between test results obtained under specified intermediate precisionconditions. E1773.1.3.1 DiscussionThe specific measure and the specific conditions must be specified for each intermediate measure of precision; thus, “standarddeviation of test results among operators in a laboratory,”
22、or “day-to-day standard deviation within a laboratory for the sameoperator.”3.1.3.2 DiscussionBecause the training of operators, the agreement of different pieces of equipment in the same laboratory and the variation ofenvironmental conditions with longer time intervals all depend on the degree of w
23、ithin- laboratory control, the intermediatemeasures of precision are likely to vary appreciably from laboratory to laboratory. Thus, intermediate precisions may be morecharacteristic of individual laboratories than of the test method.3.1.4 test result, nthe value of a characteristic obtained by carr
24、ying out a specified test method. E22823.1.5 repeatability, nprecision under repeatability conditions. E1773.2 Definitions of Terms Specific to This Standard:3.2.1 uncertainty control chart, ncontrol chart that includes control limits based on the variation attributed to the uncertaintyof the test m
25、ethod.4. Summary of Practice4.1 Astandard material or control sample is measured repeatedly over time.The presumption of this practice is that the variationexperienced on this material will be indicative of the laboratory total expected variation. Incorporation of specific known orpotential sources
26、of variation in the testing program is encouraged.4.2 A control chart is prepared and the results are evaluated to identify short-term variation and longer-term variation. Thesedata can then be used to determine an estimate of uncertainty standard deviation.4.3 Laboratories already having control ch
27、art procedures in place may use existing data.4.4 Ongoing monitoring of the test method is conducted using an uncertainty control chart.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.E2554 1324. Significance and Use4.1
28、 This practice provides one way for a laboratory to develop data-based Type A estimates of uncertainty as referred to inSection A22 in Form and Style of ASTM Standards.4.2 Laboratories accredited under ISOISO/IEC 17025 are required to present uncertainty estimates for their test results. Thispractic
29、e provides procedures that use test results to develop uncertainty estimates for an individual laboratory.4.3 Generally, these test results will be from a single sample of stable and homogeneous material known as a control or checksample.4.4 The true value of the characteristic(s) of the control sam
30、ple being measured will ordinarily be unknown. However, thismethodology may also be used if the control sample is a reference material, in which case the test method bias may also beestimated and incorporated into the uncertainty estimate. Many test methods do not have true reference materials avail
31、able toprovide traceable chains of uncertainty estimation.4.5 This practice also allows for ongoing monitoring of the laboratory uncertainty. As estimates of the level of uncertaintychange, possibly as contributions to uncertainty are identified and minimized, revision to the laboratory uncertainty
32、will bepossible.5. General Considerations5.1 Materials to be Used:5.1.1 This methodology requires a quantity of stable and homogeneous material which will serve as the source of controlsamples (sometimes called check samples). The material shall be similar in composition to the samples of material r
33、outinelyanalyzed by this test method in this laboratory. By stable it is assumed that the test results obtained from this material should beconsistent over the time interval that this material will be used. By homogeneous it is assumed that samples taken from the materialsource will not have a signi
34、ficant variation in the characteristic measured by the test method.5.1.2 For destructive testing of control sample materials, provision shall be made for depletion and replacement of the controlsample material.5.1.2.1 In some cases, the test method may be nondestructive and the same material may be
35、reused indefinitely.5.1.2.2 In other cases, the material may be used up, deteriorate, or otherwise gradually change.5.1.3 The test method should describe the best practices for preparing and storing the control material and taking the controlsamples.5.2 Test Conditions:5.2.1 An uncertainty estimatio
36、n program should be designed to include all known sources of variation, such as operators(analysts), equipment, reagents, and so forth, and these should be deliberately incorporated into the design of the program. Ingeneral, these sources of variation will be defined (including acceptable tolerances
37、) by the test method.5.2.2 In cases in which control over such variations is not possible or undefined, at least 30 to 50 sampling periods shall beevaluated to permit environmental and other factors to be incorporated in the overall estimate.6. Overall ProcedureControl Charting Methods6.1 General co
38、ncepts of control charts are described elsewhere, such elsewhere. For more information, see Practice E2587 asin well as Manual 7A.46.2 The general procedure involves two major phases: Preliminary and Monitoring.6.2.1 Preliminary Phase:6.2.1.1 This phase begins with an initial collection of test resu
39、lts.6.2.1.2 Preliminary control charts are then prepared and examined. These charts are evaluated to determine if the process is ina state of statistical control.The usual principles of control charting utilize short-term variability to estimate the limits within whichsamples of test results should
40、vary. For control sample programs this short-term variability is equivalent to repeatability precision.It is expected, however, that additional contributions to variation will be present over time and therefore additional variation,equivalent to intermediate precision, will be encountered.6.2.1.3 An
41、 estimate of uncertainty standard deviation is developed.6.2.1.4 An uncertainty control chart is then prepared to monitor future sample results.6.2.2 Monitoring Phase:6.2.2.1 The proposed uncertainty control chart is used to provide evidence that the estimate of uncertainty is not exceeding theestim
42、ated value.6.2.2.2 The estimate of uncertainty should be periodically re-evaluated.6.2.2.3 Where appropriate, it is recommended that a standard control chart also be maintained to determine whether thevariation over time has been reduced to the level of short-term variation (repeatability).4 Manual
43、on Presentation of Data and Control Chart Analysis: 7th Edition, , ASTM International, West Conshohocken, PA, 2001.E2554 1336.3 Two types of control charting methods are recommended to develop estimates of uncertainty. These include:6.3.1 Mean (Xbar) and range or standard deviation charts are used w
44、hen multiple test results are conducted in each time period.6.3.2 Individual charts (IndX) are used when single test results are obtained in each time period.6.4 Variation Estimates:6.4.1 Either a range chart or a standard deviation chart may be used to estimate the short-term variability when multi
45、ple assaysare conducted under repeatability conditions per time period. An estimate from the control chart data can be compared to otherestimates of repeatability (within laboratory, short-term variation) if available.6.4.2 Sample averages are examined and may provide estimates of variation caused b
46、y other factors. Such factors may includeenvironmental effects, operator factors, reagents, or instruments.6.5 Systematic Procedures:6.5.1 Specifically designed experiments can be used to ensure all known sources of variation, such as operators (analysts),equipment, reagents, or instruments are inco
47、rporated in the general study.6.5.2 The data generated from this program is available for additional uses, such as control charting to evaluate trends,stratification by analysis, or stratification by equipment to identify training or maintenance needs or both.7. Specific Procedures7.1 Multiple Test
48、Results Generated perPer Time Period:7.1.1 A specified number of independent test results are taken during each time period. Generally this number is 5 or less. Itis preferred that at least 25 sets of test results be obtained before developing the charts.7.1.2 Either a range chart or a standard devi
49、ation chart is prepared.This is examined for special cause variation. If the variabilityappears random then an estimate of repeatability is computed. This may be done by pooling the sums of squares, using the averagestandard deviation, or using the average range.NOTE 1If the ranges or standard deviations are zero in most of the samples, then this estimate of repeatability standard deviation is suspect andprobably unusable. This is usually the result of insufficient resolution of the measurement system in use or severe rounding. An estimate based on theminimum interv
