Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
|Publication Date:||15 January 2008|
This practice establishes uniform standards for estimating and expressing the precision and bias of applicable test methods for Committee D19 on Water.
Except as specified in 1.3, 1.4, and 1.5, 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.
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.
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.
If uniform samples are not feasible under any circumstances, a statement of single-operator precision will meet the requirements of this practice. Whenever possible, this statement should be developed from data generated by independent multiple operators, each doing replicate analyses on independent samples (of a specific matrix type), which generally fall within specified concentration ranges (see 188.8.131.52 (3)).
This practice is not applicable to methodology involving continuous sampling or continuous measurement, or both, of specific constituents and properties.
This practice is also not applicable to open-channel flow measurements.
A collaborative study that satisfied the requirements of the version of this practice in force when the study was conducted will continue to be considered an adequate basis for the precision-and-bias statement required in each test method. If the study does not satisfy the current minimum requirements for a collaborative study, a statement listing the study's deficiencies and a reference to this paragraph shall be included in the precision-and-bias statement as the basis for an exemption from the current requirements.
This paragraph relates to special exemptions not clearly acceptable under 1.3 or 1.4. With the approval of Committee D19 on the recommendation of the Results Advisor and the Technical Operations Section of the Executive Subcommittee of Committee D19, a statement giving a compelling reason why compliance with all or specific points of this practice cannot be achieved will meet both ASTM requirements (1)2 and the related requirements of this practice. In addition, Committee D19, through a Main Committee ballot, may approve publication of a "Preliminary" Standard Method for a period not to exceed 5 years. Preliminary Standards must contain a minimum of a single-operator precision-and-bias statement and a Quality Control section based on the single operator data. Publication of a Preliminary Standard is conditional on the approval of a full D 2777 collaborative study design for the standard. Precision-and-bias statements authorized by this paragraph shall include the date of approval by Committee D19.
In principle, all test methods are covered by this practice.
In Section 12 this practice shows exemplary precisionand- bias-statement formats for: (1) test methods yielding a numerical measure, (2) test methods yielding a non-numerical report of success or failure based on criteria specified in the procedure, and (3) test methods specifying that procedures in another ASTM test method are to be used with only insignificant modifications.
All studies, even those exempt from some requirements under 1.3 or 1.5, shall receive approval from the Results Advisor before being conducted (see Section 8) and after completion (see Section 13).
This practice satisfies the QC requirements of Practice D 5847.
It is the intent of this practice that task groups make every effort to retain all the data from their round-robin studies. Values should not be eliminated unless solid evidence exists for their exclusion. The Results Advisor should work closely with the task groups to effect this goal.