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ASTM D 2777 Document Information:
Title
Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
ASTM International
Publication Date:
Jan 15, 2008
Scope:
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 7.2.5.2 (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.
Keywords:
- collaborative study
- detection
- interlaboratory study
- method bias
- method precision
- method recovery
- quantitation
- round-robin study
- statistical analysis
- Youden study design
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