ASTM D7366-08(2013)
(Practice)Standard Practice for Estimation of Measurement Uncertainty for Data from Regression-based Methods
Standard Practice for Estimation of Measurement Uncertainty for Data from Regression-based Methods
SIGNIFICANCE AND USE
5.1 Appropriate application of this practice should result in an estimate of the test-method’s uncertainty (at any concentration within the working range), which can be compared with data-quality objectives to see if the uncertainty is acceptable.
5.2 With data sets that compare recovered concentration with true concentration, the resulting regression plot allows the correction of the recovery data to true values. Reporting of such corrections is at the discretion of the user.
5.3 This practice should be used to estimate the measurement uncertainty for any application of a test method where measurement uncertainty is important to data use.
SCOPE
1.1 This practice establishes a standard for computing the measurement uncertainty for applicable test methods in Committee D19 on Water. The practice does not provide a single-point estimate for the entire working range, but rather relates the uncertainty to concentration. The statistical technique of regression is employed during data analysis.
1.2 Applicable test methods are those whose results come from regression-based methods and whose data are intra-laboratory (not inter-laboratory data, such as result from round-robin studies). For each analysis conducted using such a method, it is assumed that a fixed, reproducible amount of sample is introduced.
1.3 Calculation of the measurement uncertainty involves the analysis of data collected to help characterize the analytical method over an appropriate concentration range. Example sources of data include: 1) calibration studies (which may or may not be conducted in pure solvent), 2) recovery studies (which typically are conducted in matrix and include all sample-preparation steps), and 3) collections of data obtained as part of the method’s ongoing Quality Control program. Use of multiple instruments, multiple operators, or both, and field-sampling protocols may or may not be reflected in the data.
1.4 In any designed study whose data are to be used to calculate method uncertainty, the user should think carefully about what the study is trying to accomplish and much variation should be incorporated into the study. General guidance on designing studies (for example, calibration, recovery) is given in Appendix A. Detailed guidelines on sources of variation are outside the scope of this practice, but general points to consider are included in Appendix B, which is not intended to be exhaustive. With any study, the user must think carefully about the factors involved with conducting the analysis, and must realize that the computed measurement uncertainty will reflect the quality of the input data.
1.5 Associated with the measurement uncertainty is a user-chosen level of statistical confidence.
1.6 At any concentration in the working range, the measurement uncertainty is plus-or-minus the half-width of the prediction interval associated with the regression line.
1.7 It is assumed that the user has access to a statistical software package for performing regression. A statistician should be consulted if assistance is needed in selecting such a program.
1.8 A statistician also should be consulted if data transformations are being considered.
1.9 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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Designation: D7366 − 08 (Reapproved 2013)
Standard Practice for
Estimation of Measurement Uncertainty for Data from
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Regression-based Methods
This standard is issued under the fixed designation D7366; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope analysis, and must realize that the computed measurement
uncertainty will reflect the quality of the input data.
1.1 This practice establishes a standard for computing the
1.5 Associated with the measurement uncertainty is a user-
measurement uncertainty for applicable test methods in Com-
chosen level of statistical confidence.
mittee D19 on Water. The practice does not provide a single-
point estimate for the entire working range, but rather relates
1.6 Atanyconcentrationintheworkingrange,themeasure-
the uncertainty to concentration. The statistical technique of
ment uncertainty is plus-or-minus the half-width of the predic-
regression is employed during data analysis.
tion interval associated with the regression line.
1.2 Applicable test methods are those whose results come
1.7 It is assumed that the user has access to a statistical
from regression-based methods and whose data are intra-
software package for performing regression. A statistician
laboratory (not inter-laboratory data, such as result from
should be consulted if assistance is needed in selecting such a
round-robinstudies).Foreachanalysisconductedusingsucha
program.
method, it is assumed that a fixed, reproducible amount of
1.8 A statistician also should be consulted if data transfor-
sample is introduced.
mations are being considered.
1.3 Calculationofthemeasurementuncertaintyinvolvesthe
1.9 This standard does not purport to address all of the
analysis of data collected to help characterize the analytical
safety concerns, if any, associated with its use. It is the
method over an appropriate concentration range. Example
responsibility of the user of this standard to establish appro-
sources of data include: 1) calibration studies (which may or
priate safety and health practices and determine the applica-
may not be conducted in pure solvent), 2) recovery studies
bility of regulatory limitations prior to use.
(which typically are conducted in matrix and include all
sample-preparation steps), and 3) collections of data obtained
2. Referenced Documents
as part of the method’s ongoing Quality Control program. Use
2
2.1 ASTM Standards:
of multiple instruments, multiple operators, or both, and
D1129Terminology Relating to Water
field-sampling protocols may or may not be reflected in the
data.
3. Terminology
1.4 In any designed study whose data are to be used to
3.1 Definitions of Terms Specific to This Standard:
calculate method uncertainty, the user should think carefully
3.1.1 confidence level—the probability that the prediction
about what the study is trying to accomplish and much
interval from a regression estimate will encompass the true
variation should be incorporated into the study. General guid-
value of the amount or concentration of the analyte in a
ance on designing studies (for example, calibration, recovery)
subsequent measurement. Typical choices for the confidence
is given in Appendix A. Detailed guidelines on sources of
level are 99% and 95%.
variation are outside the scope of this practice, but general
3.1.2 fitting technique—a method for estimating the param-
points to consider are included in Appendix B, which is not
eters of a mathematical model. For example, ordinary least
intended to be exhaustive. With any study, the user must think
squares is a fitting technique that may be used to estimate the
carefully about the factors involved with conducting the
parameters a,a,a ,… of the polynomial modely=a +a x
0 1 2 0 1
2
+a x +…, based on observed {x,y} pairs. Weighted least
2
squares is also a fitting technique.
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This practice is under the jurisdiction ofASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.02 on Quality Systems,
2
Specification, and Statistics. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Jan. 1, 2013. Published January 2013. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2008. Last previous approval in 2008 as D7366 – 08. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7366-08R13. the ASTM website.
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D7366 − 08 (2013)
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