ASTM D7372-07
(Guide)Standard Guide for Analysis and Interpretation of Proficiency Test Program Results
Standard Guide for Analysis and Interpretation of Proficiency Test Program Results
SCOPE
1.1 This guide covers the analysis and interpretation of proficiency test (PT) program results. For participants in interlaboratory proficiency test (or crosscheck, check scheme, etc.) programs, this guide describes procedures for assessing participants' results relative to the PT program results and potentially improving the laboratory's testing performance based on the assessment findings and insights (see ). For the committees responsible for the test methods included in interlaboratory proficiency testing programs, this guide describes procedures for assessing the industry's ability to perform test methods, and for potentially identifying needs for test method improvement (see 6.2).
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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AnAmerican National Standard
Designation: D7372 – 07
Standard Guide for
Analysis and Interpretation of Proficiency Test Program
Results
This standard is issued under the fixed designation D7372; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (ϵ) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2 assignable cause, n—factor that contributes to varia-
tion and that is feasible to detect and identify. E456
1.1 This guide covers the analysis and interpretation of
3.1.3 bias, n—systematic error that contributes to the dif-
proficiency test (PT) program results. For participants in
ferencebetweenapopulationmeanofthemeasurementsortest
interlaboratory proficiency test (or crosscheck, check scheme,
results and an accepted reference or true value. E177, E456
etc.) programs, this guide describes procedures for assessing
3.1.4 control limits, n—limits on a control chart that are
participants’ results relative to the PT program results and
used as criteria for signaling the need for action or for judging
potentially improving the laboratory’s testing performance
whether a set of data does or does not indicate a state of
based on the assessment findings and insights (see 6.1). For the
statistical control. E456
committees responsible for the test methods included in
3.1.5 in-statistical-control, adj—process, analytical mea-
interlaboratory proficiency testing programs, this guide de-
surement system, or function that exhibits variations that can
scribes procedures for assessing the industry’s ability to
only be attributable to common cause. D6299
perform test methods, and for potentially identifying needs for
3.1.6 proficiency testing, n—determination of a laboratory’s
test method improvement (see 6.2).
testing capability by participation in an interlaboratory cross-
1.2 This standard does not purport to address all of the
check program D6299
safety concerns, if any, associated with its use. It is the
3.1.7 Z-score, n—standardized and dimensionless measure
responsibility of the user of this standard to establish appro-
of the difference between an individual result in a data set and
priate safety and health practices and determine the applica-
the arithmetic mean of the dataset, re-expressed in units of
bility of regulatory limitations prior to use.
standard deviation of the dataset (by dividing the actual
2. Referenced Documents difference from the mean by the standard deviation for the data
set). D6299
2.1 ASTM Standards:
3.1.8 Z`-score, n—measure similar to the Z-score except
D6299 Practice for Applying Statistical Quality Assurance
that the PT program standard deviation is replaced with one
and Control Charting Techniques to Evaluate Analytical
that takes into account the site precision of the laboratory. Z` is
Measurement System Performance
a valid approach when the laboratory’s site precision standard
D6792 Practice for Quality System in Petroleum Products
deviation is less than the PT program (that is, these data
and Lubricants Testing Laboratories
standard deviation) or stated otherwise when the TPI > 1.
E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
~X – X!
i
Z8 5
E456 Terminology Relating to Quality and Statistics
s
these data
ŒS~s8! 1S DD
n
3. Terminology
where:
3.1 Definitions:
Z` = site precision adjusted Z-Score,
3.1.1 accuracy, n—closeness of agreement between an
X = laboratory’s result,
observed value and an accepted reference value. E177, E456 i
X = PT average value,
s’ = site precision standard deviation estimate,
This guide is under the jurisdiction of ASTM Committee D02 on Petroleum
and
Products and Lubricants and is the direct responsibility of Subcommittee D02.94 on
s = PT Program standard deviation estimate.
these data
Coordinating Subcommittee on Quality Assurance and Statistics.
3.2 Definitions of Terms Specific to This Standard:
Current edition approved July 1, 2007. Published July 2007. DOI: 10.1520/
D7372-07. 3.2.1 common (chance, random) cause, n—for quality as-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
suranceprograms,oneofgenerallynumerousfactors,individu-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ally of relatively small importance, that contributes to varia-
Standards volume information, refer to the standard’s Document Summary page on
tion, and that is not feasible to detect or control. D6299
the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
D7372 – 07
3.2.2 these test data, n—term used by the ASTM Interna- its PT records. Verify that the units for the data reported for
tional D02 PT program to identify statistical results calculated your laboratory are the same as that requested by the PT
from the data submitted by program participants. program. Report discrepancies to the PT program contacts.
3.2.3 site precision (R’), n—value below which the absolute Investigate to determine the root cause of the problem.
difference between two individual test results obtained under
6.1.2 Missing Data—If data and corresponding results are
site precision conditions may be expected to occur with a
not present when they are clearly expected, then investigate to
probability of approximately 0.95 (95 %). It is defined as 2.77
determine the cause. In some cases it could be an error within
times the standard deviation of results obtained under site
the PT program data entry system, or it could be an omission
precision conditions. D6299
on the part of the laboratory.
3.2.4 site precision conditions, n—conditions under which
6.1.3 Rejected Data—Perform an investigation for each
test results are obtained by one or more operators in a single
instance where laboratory data are rejected by the PT program
site location practicing the same test method on a single
datatreatmentprocess.Attempttodeterminetherootcauseand
measurement system which may comprise multiple instru-
take corrective actions as needed. Document all such investi-
ments, using test specimens taken at random from the same
gations and outcomes. Causes should be shared with the
sample of material, over an extended period of time spanning
laboratory staff performing the testing. Guidelines on conduct-
at least a 15-day interval. D6299
ing these types of investigations are available in Practice
3.3 Symbols:
D6299.
3.3.1 I—individual observation (as in I-chart).
6.1.4 Warnings/Alerts on Data—The ASTM International
3.3.2 QC—quality control.
D02 PT programs provide comments (that is, Notes 1 to 3 in
3.3.3 R’—site precision.
each Table of Results) that warn participants when their result
is:
4. Summary of Guide
Note 1—outside 3-sigma range for these test data
Note 2—outside 3-sigma range forASTM reproducibility
4.1 Petroleum and petroleum product samples are regularly
Note 3—When the Z-score is outside the range -2 to 2
analyzed by specified standard test methods as part of a
proficiencytestprogram.Thisguideprovidesalaboratorywith
Investigations should also be conducted when any of these
the tools and procedures for evaluating their results from the
warning situations occur. The priority for conducting investi-
PT program. Techniques are presented to screen, plot, and
gations should be for Note 1 > Note 2 > Note 3. Note 1
interpret test results in accordance with industry-accepted
indicates that the laboratory is out-of-control with respect to
practices.
the data set (with the rejected data removed), which is a
potentially serious situation with respect to the quality control
5. Significance and Use
performance of the corresponding standard test method. A
similar argument could also be made for Note 2. Note 3 is a
5.1 This guide can be used to evaluate the performance of a
less severe situation, but should be investigated from a con-
laboratory or group of laboratories participating in an inter-
tinuous improvement standpoint.
laboratory proficiency test (PT) program involving petroleum
and petroleum products.
NOTE 1—If the user notices that the majority of the laboratories have
5.2 Data accrued, using the techniques included in this
been cited with a Note 2, then an investigation may not produce any
guide, provide the ability to monitor analytical measurement
meaningful corrective actions. This occurrence may be the result of the
system precision and bias. These data are useful for updating
precision statement not accurately reflecting the variability of the test
method and should be addressed by the subcommittee responsible for the
standard test methods, as well as for indicating areas of
method.Also, if theAnderson-Darling statistic is >1.3, then the “Note 2”
potential measurement system improvement for action by the
flag may not be valid.
laboratory.
5.3 Reference is made in this standard to the ASTM
6.1.5 Z-score—The Z-score calculated for each datum sub-
International Interlaboratory Cross-Check Program on Petro-
mitted by the laboratory should be reviewed with respect to the
leum Pro
...
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