ASTM D7782-13
(Practice)Standard Practice for Determination of the 99 %/95 % Critical Level (WCL) and a Reliable Detection Estimate (WDE) Based on Within-laboratory Data (Withdrawn 2022)
Standard Practice for Determination of the 99 %/95 % Critical Level (WCL) and a Reliable Detection Estimate (WDE) Based on Within-laboratory Data (Withdrawn 2022)
SIGNIFICANCE AND USE
5.1 This practice can be used in a single laboratory for trace analysis (that is, where: 1) there are concentrations near the lower limit of the method and 2) the measurements system’s capability to discriminate analyte presence from analyte absence is of interest). In these testing situations, a reliable estimate of the minimum level at which there is confidence that detection of the analyte by the method represents true presence of the analyte in the sample is key. Where within-laboratory detection is important to data use, the WDE procedure should be used to establish the within-laboratory detection capability for each unique application of a method.
5.2 When properly applied, the WDE procedure ensures that the 99 %/95 % WDE has the following properties:
5.2.1 Routinely Achievable Detection—The laboratory is able to attain detection performance routinely, using studied measurement systems, without extraordinary effort, and therefore at reasonable cost. This property is needed for a detection limit to be practically useful while scientifically sound. Representative equipment and analysts must be included in the study that generates the data to calculate the WDE.
5.2.2 Inclusion of Routine Sources of Error—If appropriate data are used in calculation, the WDE practice will realistically account for sources of variation and bias common to the measurement process and routine for sample analysis. These sources include, but are not limited to: 1) intrinsic instrument noise, 2) some typical amount of carryover error, and 3) differences in analysts, sample preparation, and instruments (including signal-processing methods and software versions).
5.2.3 Exclusion of Avoidable Sources of Error—The WDE practice excludes avoidable sources of bias and variation, (that is, those which can reasonably be avoided in routine field measurements). Avoidable sources would include, but are not limited to: 1) inappropriate modifications to the method, the sample, measurement p...
SCOPE
1.1 This practice provides a procedure for computing a 99 %/95 % Within-laboratory Detection Estimate (WDE) and the associated critical level/value (WCL). The WDE is the minimum concentration, with false positives and false negative appropriately controlled, such that values above these minimums are reliable detections. The WCL is the point at which only false positives are controlled appropriately. A false positive is the reporting of an analyte as present when the analyte is not actually present; false negatives are reports of analyte absence when the analyte is actually present. This practice is distinguished from the Interlaboratory Detection Estimate (IDE) practice in that the IDE Standard utilizes data from multiple, independent laboratories, while this practice is for use by a single laboratory. The IDE would be utilized where interlaboratory issues are of concern (for example, limits for published methods); this practice (and values derived from it) are applicable where the results from a single laboratory, single operator, single instrument, etc. are involved (for example, in understanding, censoring and reporting data).
1.2 The establishment of a WDE involves determining the concentration below which the precision and bias of an analytical procedure indicates insufficient confidence in false-positive and false-negative control to assert detection of the analyte in the future analysis of an unknown number of samples. Most traditional approaches attempt to determine this detection “limit” by estimating precision at only a single, arbitrary point. The WDE approach is intended to be a more technically rigorous replacement for other approaches for estimating detection limits. The WDE practice addresses a number of critical issues that are ignored in other approaches.
1.2.1 First, rather than making a single-point estimate of precision, the WDE protocol requires an estimate of precision at multiple points in th...
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7782 − 13
Standard Practice for
Determination of the 99 %/95 % Critical Level (WCL) and a
Reliable Detection Estimate (WDE) Based on Within-
1
laboratory Data
This standard is issued under the fixed designation D7782; 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.
Note—Balloted information was included and the year date changed on March 28, 2013.
1. Scope at multiple points in the analytical range, especially in the
range of the expected detection limit. These estimates are then
1.1 This practice provides a procedure for computing a
used to create an appropriate model of the method’s precision.
99%⁄95% Within-laboratory Detection Estimate (WDE) and
This approach is a more credible way to determine the point
the associated critical level/value (WCL). The WDE is the
where relative precision has become too large for reliable
minimumconcentration,withfalsepositivesandfalsenegative
detection. This process requires more data than has been
appropriately controlled, such that values above these mini-
historically required by single-point approaches or by pro-
mums are reliable detections. The WCL is the point at which
cesses for modeling the relationship between standard devia-
only false positives are controlled appropriately. A false posi-
tion and concentration.
tive is the reporting of an analyte as present when the analyte
is not actually present; false negatives are reports of analyte
1.2.2 Second, unlike most other approaches, the WDE
absence when the analyte is actually present. This practice is
process accounts for analytical bias at the concentrations of
distinguished from the Interlaboratory Detection Estimate
interest. The relationship of true concentration to measured
(IDE) practice in that the IDE Standard utilizes data from
concentration (that is, the recovery curve) is established and
multiple,independentlaboratories,whilethispracticeisforuse
utilized in converting from as-measured to true concentration.
by a single laboratory. The IDE would be utilized where
1.2.3 Third, most traditional approaches to detection limits
interlaboratory issues are of concern (for example, limits for
only address the issue of false positives. Although false
published methods); this practice (and values derived from it)
negatives may not be of concern in some data uses, there are
areapplicablewheretheresultsfromasinglelaboratory,single
many uses where understanding and/or control of false nega-
operator, single instrument, etc. are involved (for example, in
tives is important. Without the false-negative-control
understanding, censoring and reporting data).
information, data reported with just a critical-level value are
1.2 The establishment of a WDE involves determining the
incompletely described and the qualities of data at these levels
concentration below which the precision and bias of an
incompletely disclosed.
analytical procedure indicates insufficient confidence in false-
1.2.4 Fourth and last, the WDE standard utilizes a
positive and false-negative control to assert detection of the
statistical-tolerance interval in calculations, such that future
analyte in the future analysis of an unknown number of
measurements may reasonably be expected to be encompassed
samples. Most traditional approaches attempt to determine this
by the WDE 90% of the time. Many older approaches have
detection “limit” by estimating precision at only a single,
usedthestatisticalconfidenceinterval,whichisnotintendedto
arbitrary point. The WDE approach is intended to be a more
encompass individual future measurements, and has been
technically rigorous replacement for other approaches for
misunderstood and misapplied. Procedures using the confi-
estimating detection limits. The WDE practice addresses a
dence interval cannot provide the stated control when the
number of critical issues that are ignored in other approaches.
detection-limit value is applied to future sample results; such
1.2.1 First, rather than making a single-point estimate of
application is the primary use of these values.
precision, the WDE protocol requires an estimate of precision
1.3 To summarize, the WDE is computed to be the lowest
1 true concentration at which there is 90% confidence that a
This practice is under the jurisdiction ofASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.02 on Quality Systems,
single (future) measurement (from the studied laboratory) will
Specification, and Statistics.
have a true detection probability of at least 95% and a true
Current edition approved March 28, 2013. Published April 2013. Origin
...
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