1、Designation: D 7372 07An American National StandardStandard Guide forAnalysis and Interpretation of Proficiency Test ProgramResults1This standard is issued under the fixed designation D 7372; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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 guide covers the analysis and interpretation ofproficiency test (PT) program results. For p
3、articipants ininterlaboratory proficiency test (or crosscheck, check scheme,etc.) programs, this guide describes procedures for assessingparticipants results relative to the PT program results andpotentially improving the laboratorys testing performancebased on the assessment findings and insights (
4、see 6.1). For thecommittees responsible for the test methods included ininterlaboratory proficiency testing programs, this guide de-scribes procedures for assessing the industrys ability toperform test methods, and for potentially identifying needs fortest method improvement (see 6.2).1.2 This stand
5、ard 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 AS
6、TM Standards:2D 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformanceD 6792 Guide for Quality System in Petroleum Productsand Lubricants Testing LaboratoriesE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 4
7、56 Terminology Relating to Quality and Statistics3. Terminology3.1 Definitions:3.1.1 accuracy, ncloseness of agreement between anobserved value and an accepted reference value. E 177,E 4563.1.2 assignable cause, nfactor that contributes to varia-tion and that is feasible to detect and identify. E 45
8、63.1.3 bias, nsystematic error that contributes to the dif-ference between a population mean of the measurements or testresults and an accepted reference or true value. E 177, E 4563.1.4 control limits, nlimits on a control chart that areused as criteria for signaling the need for action or for judg
9、ingwhether a set of data does or does not indicate a state ofstatistical control. E 4563.1.5 in-statistical-control, adjprocess, analytical mea-surement system, or function that exhibits variations that canonly be attributable to common cause. D 62993.1.6 proficiency testing, ndetermination of a lab
10、oratorystesting capability by participation in an interlaboratory cross-check program D 62993.1.7 Z-score, nstandardized and dimensionless measureof the difference between an individual result in a data set andthe arithmetic mean of the dataset, re-expressed in units ofstandard deviation of the data
11、set (by dividing the actualdifference from the mean by the standard deviation for the dataset). D 62993.1.8 Z8-score, nmeasure similar to the Z-score exceptthat the PT program standard deviation is replaced with onethat takes into account the site precision of the laboratory. Z8 isa valid approach w
12、hen the laboratorys site precision standarddeviation is less than the PT program (that is, these datastandard deviation) or stated otherwise when the TPI 1.Z8 5Xi X!Ss8!21 Ssthese data2nDDwhere:Z8 = site precision adjusted Z-Score,Xi= laboratorys result,X = PT average value,s = site precision standa
13、rd deviation estimate,andsthese data= PT Program standard deviation estimate.3.2 Definitions of Terms Specific to This Standard:3.2.1 common (chance, random) cause, nfor quality as-surance programs, one of generally numerous factors, individu-ally of relatively small importance, that contributes to
14、varia-tion, and that is not feasible to detect or control. D 62991This guide is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibility of Subcommittee D02.94 onCoordinating Subcommittee on Quality Assurance and Statistics.Current edition app
15、roved July 1, 2007. Published July 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.1Copyright ASTM Inter
16、national, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2 these test data, nterm used by the ASTM Interna-tional D02 PT program to identify statistical results calculatedfrom the data submitted by program participants.3.2.3 site precision (R), nvalue below w
17、hich the absolutedifference between two individual test results obtained undersite precision conditions may be expected to occur with aprobability of approximately 0.95 (95 %). It is defined as 2.77times the standard deviation of results obtained under siteprecision conditions. D 62993.2.4 site prec
18、ision conditions, nconditions under whichtest results are obtained by one or more operators in a singlesite location practicing the same test method on a singlemeasurement system which may comprise multiple instru-ments, using test specimens taken at random from the samesample of material, over an e
19、xtended period of time spanningat least a 15-day interval. D 62993.3 Symbols:3.3.1 Iindividual observation (as in I-chart).3.3.2 QCquality control.3.3.3 Rsite precision.4. Summary of Guide4.1 Petroleum and petroleum product samples are regularlyanalyzed by specified standard test methods as part of
20、aproficiency test program. This guide provides a laboratory withthe tools and procedures for evaluating their results from thePT program. Techniques are presented to screen, plot, andinterpret test results in accordance with industry-acceptedpractices.5. Significance and Use5.1 This guide can be use
21、d to evaluate the performance of alaboratory or group of laboratories participating in an inter-laboratory proficiency test (PT) program involving petroleumand petroleum products.5.2 Data accrued, using the techniques included in thisguide, provide the ability to monitor analytical measurementsystem
22、 precision and bias. These data are useful for updatingstandard test methods, as well as for indicating areas ofpotential measurement system improvement for action by thelaboratory.5.3 Reference is made in this standard to the ASTMInternational Interlaboratory Cross-Check Program on Petro-leum Produ
23、cts and Lubricants. Program reports containingsimilarly displayed results and statistical treatments may beavailable in other PT programs.6. Procedure6.1 Analysis and Interpretation by the ParticipatingLaboratoryThe laboratory should review the results pub-lished for each proficiency test program an
24、d for each testmethod or parameter for which the laboratory submitted data.This section covers the evaluations and analyses that thelaboratory should consider during their review of proficiencytest results.6.1.1 Reported versus Submitted DataCheck to verifythat the values ascribed to the laboratory
25、in the Proficiency Test(PT) report agree with the values recorded by the laboratory inits PT records. Verify that the units for the data reported foryour laboratory are the same as that requested by the PTprogram. Report discrepancies to the PT program contacts.Investigate to determine the root caus
26、e of the problem.6.1.2 Missing DataIf data and corresponding results arenot present when they are clearly expected, then investigate todetermine the cause. In some cases it could be an error withinthe PT program data entry system, or it could be an omissionon the part of the laboratory.6.1.3 Rejecte
27、d DataPerform an investigation for eachinstance where laboratory data are rejected by the PT programdata treatment process.Attempt to determine the root cause andtake corrective actions as needed. Document all such investi-gations and outcomes. Causes should be shared with thelaboratory staff perfor
28、ming the testing. Guidelines on conduct-ing these types of investigations are available in PracticeD 6299.6.1.4 Warnings/Alerts on DataThe ASTM InternationalD02 PT programs provide comments (that is, Notes 1 to 3 ineach Table of Results) that warn participants when their resultis:Note 1outside 3-sig
29、ma range for these test dataNote 2outside 3-sigma range for ASTM reproducibilityNote 3When the Z-score is outside the range -2 to 2Investigations should also be conducted when any of thesewarning situations occur. The priority for conducting investi-gations should be for Note 1 Note 2 Note 3. Note 1
30、indicates that the laboratory is out-of-control with respect tothe data set (with the rejected data removed), which is apotentially serious situation with respect to the quality controlperformance of the corresponding standard test method. Asimilar argument could also be made for Note 2. Note 3 is a
31、less severe situation, but should be investigated from a con-tinuous improvement standpoint.NOTE 1If the user notices that the majority of the laboratories havebeen cited with a Note 2, then an investigation may not produce anymeaningful corrective actions. This occurrence may be the result of thepr
32、ecision statement not accurately reflecting the variability of the testmethod and should be addressed by the subcommittee responsible for themethod. Also, if the Anderson-Darling statistic is 1.3, then the “Note 2”flag may not be valid.6.1.5 Z-scoreThe Z-score calculated for each datum sub-mitted by
33、 the laboratory should be reviewed with respect to thefollowing:6.1.5.1 Sign and Magnitude of Z-scoreThe sign (“+” or“-”) of the statistic reflects the relative bias of the individualresult versus the mean of the sample group. Z-score valuesfalling in the ranges of 60-1, 1 to 2, 2 to 3, and 3 can be
34、compared to control chart values falling in the ranges betweenthe mean and 1-sigma, 1 to 2-sigma, 2 to 3-sigma, and 3-sigma. For normally distributed data, there is an expectationthat about 68% of the data will lie in the -1 sigma to +1 sigmarange, about 95% in the -2 sigma to +2 sigma range, and 99
35、%in the -3 to +3 sigma range. The further a laboratorys Z-scoreis from zero, the greater the relative bias and lower theprobability that the data is considered within statistical control.Conduct investigations to determine the cause of any perceivedbias as needed.D73720726.1.5.2 Trend of Z-scores fr
36、om Previous RoundsRecordthe Z-score values for each test method (parameter) forsuccessive PT program rounds on a control chart to show thetrend over time. The lab can use the run rules promulgated inPractice D 6299 to evaluate any observed trends. Conductinvestigations to determine causes as needed.
37、6.1.5.3 Average Z-scoreCalculate the average Z-score fora series over a selected time period. The sign and magnitude ofthis result is an indication of the long-term relative bias.Conduct investigations to determine the cause of any perceivedbias as needed.6.1.6 Z8-scoreThe analysis of any Z8 calcula
38、ted by thelaboratory should be evaluated as described in 6.1.5.3 for theZ-score.6.1.7 TPI (Industry)Consider the TPI (Industry) valuereported for the data set along with the corresponding Z-scorefor the laboratorys result (reference Guide D 6792).6.1.7.1 Broad ImplicationsConsider the following fori
39、nterpreting the TPI (Industry): 1.2 The performance of the group providing data is probably satisfac-tory relative to the corresponding ASTM published precision.0.8 to 1.2 The performance of the group providing data may be marginal.Each laboratory should consider reviewing the test method proce-dure
40、s to identify opportunities for improvement.3(or 63), and evaluate the factors that may be contrib-uting to this performance. This may involve targeting theselaboratories with questionnaires to gather appropriate informa-tion. Consultation with test method experts is generally helpfulin interpreting
41、 results from these investigations.7. Report7.1 Laboratories and working groups should document theirinvestigations. In the spirit of continuous improvement, labo-ratories and working groups are encouraged to share theirfindings from their investigations and analyses.8. Keywords8.1 proficiency testi
42、ng; quality control; test performanceindex; Z-scoreAPPENDIX(Nonmandatory Information)X1. CHECKLIST FOR INVESTIGATING THE ROOT CAUSE OF UNSATISFACTORY ANALYTICAL PERFORMANCEX1.1 To identify why a laboratorys data may have beenconsidered a statistical outlier or to improve the precision, orboth, the f
43、ollowing action items (not necessarily in the order ofpreference) are suggested. There may be additional ways toimprove the performance.X1.1.1 Check the results for typos, calculation errors, andtranscription errors.X1.1.2 Reanalyze the sample; compare to site precision, or,if not available, test me
44、thod repeatability.X1.1.3 Check the sample for homogeneity, contamination,or that a representative sample has been analyzed.X1.1.4 Review the test method, and ensure that the latestversion of the ASTM test method is being used. Check theprocedure step-by-step with the analyst.D7372073X1.1.5 Check th
45、e instrument calibration.X1.1.6 Check the statistical quality control chart to see if theproblem developed earlier.X1.1.7 Check the quality of the reagents and standards usedand whether or not they are expired or contaminated.X1.1.8 Check the equipment for proper operation againstthe vendors operati
46、ng manual.X1.1.9 Perform maintenance or repairs, or both, on theequipment following guidelines established by the vendor.X1.1.10 After the problem has been resolved, analyze acertified reference material, if one is available, or the labora-tory quality control sample, to ascertain that the analytica
47、loperation is under control.X1.1.11 Provide training to new analysts and, if necessary,refresher training to experienced analysts.X1.1.12 Document the incident and the learnings for use inthe future if a similar problem occurs.ASTM International takes no position respecting the validity of any paten
48、t rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision a
49、t any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards,
