Following this practice should result in precision-and-bias statements that can be achieved by any laboratory properly using the test method studied. These precision-and-bias statements provide the basis for generic limits for use in the Quality Control section of the test method. Optionally, the detection and quantitation values provide estimates of the level at which most laboratories should be able to achieve confident detection and meet the minimum precision (expressed as relative standard deviation) expected.
The method specifies the matrices for which the test method is appropriate. The collaborative test corroborates the write-up within the limitations of the test design. An extensive test can only use representative matrices so that universal applicability cannot be implied from the results.
The fundamental assumption of the collaborative study is that the matrices tested, the concentrations tested, and the participating laboratories are a representative and fair evaluation of the scope and applicability of the test method as written.
1.1 This practice establishes uniform standards for estimating and expressing the precision and bias of applicable test methods for Committee D19 on Water. In principle, all test methods are covered by this practice.
1.2 Except as specified in 1.4, 1.5, and 1.6, this practice requires the task group proposing a new test method to carry out a collaborative study from which statements for precision (overall and single-operator standard-deviation estimates) and bias can be developed. This practice provides general guidance to task groups in planning and conducting such determinations of precision and bias.
1.3 This practice also provides guidance to task groups for conducting limited-scale collaborative studies (known as “comparability studies”) for test methods that have been revised, when such revision includes substantive modifications. Examples of substantive modifications may include, but are not limited to, changes in mandatory or allowable instrumentation, reagents, reaction times, etc.
1.3.1 Changes to applicable water matrices in the Scope of a method may constitute a substantive modification under this provision. However, recognize that even the original collaborative study may not have used all the various matrix types specified in the method’s original Scope.
1.3.2 A method's concentration-range extension that is deemed to merit additional collaborative testing (even without a method modification that would otherwise be considered substantive) shall require a full collaborative study, as described in Sections 7.1-7.5, but only at Youden-pair concentrations representative of the extended range. Note that such a collaborative study could involve as little as a single-sample Youden-pair study in a single reproducible matrix.
1.3.3 Whether a revision to a test method includes substantive modification shall be determined by consensus of the Committee.
1.4 If a full-scale collaborative study is not technically feasible, due to the nature of the test method or instability of samples, the largest feasible scaled-down collaborative study shall be conducted to provide the best possible limited basis for estimating the overall and single-operator standard deviations.
1.4.1 Examples of acceptable scaled-down studies are the local-area studies conducted by Subcommittee D19.24 on microbiological methods because of inherent sample instability. These studies involve six or more completely independent local-area analysts who can begin analysis of uniform samples at an agreed upon time.
1.4.2 If uniform samples are not feasible under any circumstances, a statement of single-operator precision will ......
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