ASTM E2554-18e1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: E2554 − 18 An American National Standard
Standard Practice for
Estimating and Monitoring the Uncertainty of Test Results
of a Test Method Using Control Chart Techniques
This standard is issued under the fixed designation E2554; 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 (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial corrections were made throughout in September 2019.
1. Scope 1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice describes techniques for a laboratory to
responsibility of the user of this standard to establish appro-
estimate the uncertainty of a test result using data from test
priate safety, health, and environmental practices and deter-
results on a control sample. This practice provides one method
mine the applicability of regulatory limitations prior to use.
for a laboratory to estimate Measurement Uncertainty in
1.9 This international standard was developed in accor-
accordance with Section A22.3 in Form and Style for ASTM
dance with internationally recognized principles on standard-
Standards.
ization established in the Decision on Principles for the
1.2 Uncertainty as defined by this practice applies to the
Development of International Standards, Guides and Recom-
capabilities of a single laboratory.Any estimate of uncertainty
mendations issued by the World Trade Organization Technical
determined through the use of this practice applies only to the
Barriers to Trade (TBT) Committee.
individual laboratory for which the data are presented.
2. Referenced Documents
1.3 The laboratory uses a well defined and established test
method in determining a series of test results. The uncertainty 2.1 ASTM Standards:
estimated using this practice only applies when the same test D5184 Test Methods for Determination of Aluminum and
method is followed. The uncertainty only applies for the Silicon in Fuel Oils by Ashing, Fusion, Inductively
materialtypesrepresentedbythecontrolsamples,andmultiple Coupled Plasma Atomic Emission Spectrometry, and
control samples may be needed, especially if the method has Atomic Absorption Spectrometry
differentprecisionfordifferentsampletypesorresponselevels. E92 Test Methods for Vickers Hardness and Knoop Hard-
ness of Metallic Materials
1.4 The uncertainty estimate determined by this practice
E177 Practice for Use of the Terms Precision and Bias in
represents the intermediate precision of test results. This
ASTM Test Methods
estimate seeks to quantify the total variation expected within a
E384 Test Method for Microindentation Hardness of Mate-
single laboratory using a single established test method while
rials
incorporating as many known sources of variation as possible.
E456 Terminology Relating to Quality and Statistics
1.5 This practice does not establish error estimates (error
E2282 Guide for Defining the Test Result of a Test Method
budget) attributed to individual factors that could influence
E2587 Practice for Use of Control Charts in Statistical
uncertainty.
Process Control
1.6 This practice describes the use of control charts to 2.2 ASTM Publications:
Form and Style for ASTM Standards
evaluatethedataobtainedandpresentsaspecialtypeofcontrol
chart to monitor the estimate of uncertainty. Manual 7A Manual on Presentation of Data and Control
Chart Analysis: 7th Edition
1.7 The system of units for this standard is not specified.
2.3 ISO Standard:
Dimensional quantities in the standard are presented only as
ISO/IEC 17025 General Requirements for the Competence
illustrations of calculation methods. The examples are not
of Testing and Calibration Laboratories
binding on products or test methods treated.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This practice is under the jurisdiction ofASTM Committee E11 on Quality and contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Statistics and is the direct responsibility of Subcommittee E11.50 on Metrology. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2018. Published April 2018. Originally the ASTM website.
approved in 2007. Last previous edition approved in 2013 as E2554 – 13. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/E2554-18E01. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E2554 − 18
3. Terminology reference material, in which case the test method bias may also
be estimated and incorporated into the uncertainty estimate.
3.1 Definitions—The terminology of Terminology E456
Many test methods do not have true reference materials
applies to this practice except as modified herein.
available to provide traceable chains of uncertainty estimation.
3.1.1 control sample, n—sample taken from a stable, homo-
geneous material for the purposes of monitoring the perfor- 4.5 This practice also allows for ongoing monitoring of the
mance of a test method in a laboratory. laboratory uncertainty.As estimates of the level of uncertainty
3.1.1.1 Discussion—The control sample material is repre- change, possibly as contributions to uncertainty are identified
sentativeoftheproducttypicallytestedinthelaboratorybythe and minimized, revision to the laboratory uncertainty will be
given test method. A control sample is run periodically using possible.
thecompletetestmethodprotocoltodevelopatestresult.Such
5. General Considerations
test results may be statistically evaluated to monitor test
5.1 Materials to be Used:
method performance over time. It is not necessary to have an
5.1.1 This methodology requires a quantity of stable and
accepted reference value assigned to the control sample mate-
homogeneous material which will serve as the source of
rial. When the current material is nearly consumed, a replace-
control samples (sometimes called check samples). The mate-
ment material should be run in parallel with the current
rial shall be similar in composition to the samples of material
material to ensure continuity in the control sample program.
routinely analyzed by this test method in this laboratory. By
3.1.2 check sample, n—see control sample.
stable it is assumed that the test results obtained from this
3.1.3 intermediate precision, n—the closeness of agreement
material should be consistent over the time interval that this
between test results obtained under specified intermediate
material will be used. By homogeneous it is assumed that
precision conditions. E177
samples taken from the material source will not have a
3.1.3.1 Discussion—The specific measure and the specific
significant variation in the characteristic measured by the test
conditions must be specified for each intermediate measure of
method.
precision; thus, “standard deviation of test results among
5.1.2 For destructive testing of control sample materials,
operators in a laboratory,” or “day-to-day standard deviation
provision shall be made for depletion and replacement of the
within a laboratory for the same operator.”
control sample material.
3.1.3.2 Discussion—Because the training of operators, the
5.1.2.1 In some cases, the test method may be nondestruc-
agreement of different pieces of equipment in the same
tive and the same material may be reused indefinitely.
laboratory and the variation of environmental conditions with
5.1.2.2 In other cases, the material may be used up,
longer time intervals all depend on the degree of within-
deteriorate, or otherwise gradually change.
laboratory control, the intermediate measures of precision are
5.1.3 The test method should describe the best practices for
likely to vary appreciably from laboratory to laboratory. Thus,
preparing and storing the control material and taking the
intermediate precisions may be more characteristic of indi-
control samples.
vidual laboratories than of the test method.
5.2 Test Conditions:
3.1.4 test result, n—the value of a characteristic obtained by
5.2.1 An uncertainty estimation program should be de-
carrying out a specified test method. E2282
signed to include all known sources of variation, such as
3.1.5 repeatability, n—precision under repeatability
operators (analysts), equipment, reagents, and so forth, and
conditions. E177
these should be deliberately incorporated into the design of the
program. In general, these sources of variation will be defined
3.2 Definitions of Terms Specific to This Standard:
(including acceptable tolerances) by the test method.
3.2.1 uncertainty control chart, n—control chart that in-
5.2.2 In cases in which control over such variations is not
cludes control limits based on the variation attributed to the
possible or undefined, at least 30 to 50 sampling periods shall
uncertainty of the test method.
be evaluated to permit environmental and other factors to be
4. Significance and Use
incorporated in the overall estimate.
4.1 This practice provides one way for a laboratory to
6. Overall Procedure—Control Charting Methods
develop data-based TypeAestimates of uncertainty as referred
6.1 General concepts of control charts are described else-
to in Section A22 in Form and Style for ASTM Standards.
where. For more information, see Practice E2587 as well as
4.2 Laboratories accredited under ISO/IEC 17025 are re-
Manual 7A.
quired to present uncertainty estimates for their test results.
6.2 The general procedure involves two major phases:
This practice provides procedures that use test results to
Preliminary and Monitoring.
develop uncertainty estimates for an individual laboratory.
6.2.1 Preliminary Phase:
4.3 Generally, these test results will be from a single sample
6.2.1.1 This phase begins with an initial collection of test
of stable and homogeneous material known as a control or
results.
check sample.
6.2.1.2 Preliminary control charts are then prepared and
4.4 The true value of the characteristic(s) of the control examined. These charts are evaluated to determine if the
sample being measured will ordinarily be unknown. However, process is in a state of statistical control. The usual principles
this methodology may also be used if the control sample is a of control charting utilize short-term variability to estimate the
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E2554 − 18
limits within which samples of test results should vary. For computed. This may be done by pooling the sums of squares,
control sample programs this short-term variability is equiva- using the average standard deviation, or using the average
lent to repeatability precision. It is expected, however, that range.
additional contributions to variation will be present over time
NOTE 1—If the ranges or standard deviations are zero in most of the
and therefore additional variation, equivalent to intermediate
samples, then this estimate of repeatability standard deviation is suspect
precision, will be encountered.
and probably unusable. This is usually the result of insufficient resolution
of the measurement system in use or severe rounding. An estimate based
6.2.1.3 An estimate of uncertainty standard deviation is
on the minimum interval size should be substituted for the zeros.As a rule
developed.
of thumb, consider replacing the zeros when more than about ⁄3 are zeros.
6.2.1.4 An uncertainty control chart is then prepared to
7.1.3 A means chart is used to examine variation among
monitor future sample results.
time periods. Limits on this chart permit comparison of
6.2.2 Monitoring Phase:
variation between time periods using repeatability as the
6.2.2.1 The proposed uncertainty control chart is used to
estimate of error.
provide evidence that the estimate of uncertainty is not
7.1.3.1 Ifthecontrolchartshowsastateofstatisticalcontrol
exceeding the estimated value.
then the uncertainty will be assumed approximately equivalent
6.2.2.2 The estimate of uncertainty should be periodically
to the repeatability standard deviation.
re-evaluated.
7.1.3.2 In most cases it will be expected that the variability
6.2.2.3 Where appropriate, it is recommended that a stan-
between means will show an “out of control” condition
dard control chart also be maintained to determine whether the
indicating that there are “special” causes of variation in
variation over time has been reduced to the level of short-term
addition to repeatability. The between means variation and
variation (repeatability).
within means repeatability estimates are then used to compute
6.3 Two types of control charting methods are recom-
an estimate of uncertainty standard deviation.
mended to develop estimates of uncertainty. These include:
7.1.4 Using the estimate of uncertainty standard deviation
6.3.1 Mean (Xbar) and range or standard deviation charts
an Uncertainty Control Chart is prepared for future monitoring
are used when multiple test results are conducted in each time
of the uncertainty. This chart may include control limits for
period.
means as a possible lower set of control limits along with the
6.3.2 Individual charts (IndX) are used when single test
uncertainty control limits based on the estimate of uncertainty.
results are obtained in each time period.
7.2 Individual Tests:
6.4 Variation Estimates:
7.2.1 Single tests are generated at each time period. Varia-
6.4.1 Either a range chart or a standard deviation chart may
tion among these results is evaluated.
be used to estimate the short-term variability when multiple
7.2.2 In some cases, it is possible to incorporate external
assays are conducted under repeatability conditions per time
estimates of repeatability obtained from prior or concurrent
period. An estimate from the control chart data can be
studies.
compared to other estimates of repeatability (within laboratory,
8. Multiple Readings Per Time Period
short-term variation) if available.
6.4.2 Sample averages are examined and may provide
8.1 Example 1—Knoop Hardness Testing:
estimates of variation caused by other factors. Such factors
8.1.1 A Knoop test is an indentation microhardness test
may include environmental effects,
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