ASTM E177-06b

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An American National Standard
Designation:E177–06b
Standard Practice for
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Use of the Terms Precision and Bias in ASTM Test Methods
This standard is issued under the fixed designation E 177; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3.1.2 accuracy, n—the closeness of agreement between a
test result and an accepted reference value.
1.1 The purpose of this practice is to present concepts
3.1.2.1 Discussion—The term accuracy, when applied to a
necessary to the understanding of the terms “precision” and
set of test results, involves a combination of a random
“bias” as used in quantitative test methods. This practice also
component and of a common systematic error or bias compo-
describes methods of expressing precision and bias and, in a
nent.
final section, gives examples of how statements on precision
3.1.3 bias, n—the difference between the expectation of the
and bias may be written for ASTM test methods.
test results and an accepted reference value.
1.2 This standard does not purport to address all of the
3.1.3.1 Discussion—Bias is the total systematic error as
safety concerns, if any, associated with its use. It is the
contrasted to random error. There may be one or more
responsibility of the user of this standard to establish appro-
systematic error components contributing to the bias. A larger
priate safety and health practices and determine the applica-
systematic difference from the accepted reference value is
bility of regulatory requirements prior to use.
reflected by a larger bias value.
2. Referenced Documents 3.1.4 intermediate precision, n—the closeness of agreement
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between test results obtained under specified intermediate
2.1 ASTM Standards:
precision conditions.
E 178 Practice for Dealing With Outlying Observations
3.1.4.1 Discussion—The specific measure and the specific
E 456 Terminology Relating to Quality and Statistics
conditions must be specified for each intermediate measure of
E 691 Practice for Conducting an Interlaboratory Study to
precision; thus, “standard deviation of test results among
Determine the Precision of a Test Method
operators in a laboratory,” or “day-to-day standard deviation
E 2282 Guide for Defining theTest Result of aTest Method
within a laboratory for the same operator.”
3. Terminology
3.1.4.2 Discussion—Because the training of operators, the
agreement of different pieces of equipment in the same
3.1 Definitions:
laboratory and the variation of environmental conditions with
3.1.1 accepted reference value, n—a value that serves as an
longer time intervals all depend on the degree of within-
agreed-upon reference for comparison, and which is derived
laboratory control, the intermediate measures of precision are
as: (1) a theoretical or established value, based on scientific
likely to vary appreciably from laboratory to laboratory. Thus,
principles, (2) an assigned or certified value, based on experi-
intermediate precisions may be more characteristic of indi-
mental work of some national or international organization, or
vidual laboratories than of the test method.
(3) a consensus or certified value, based on collaborative
3.1.5 intermediate precision conditions, n—conditions un-
experimental work under the auspices of a scientific or
der which test results are obtained with the same test method
engineering group.
usingtestunitsortestspecimenstakenatrandomfromasingle
3.1.1.1 Discussion—A national or international organiza-
quantity of material that is as nearly homogeneous as possible,
tion, referred to in (2), generally maintains measurement
and with changing conditions such as operator, measuring
standards to which the reference values obtained are traceable.
equipment, location within the laboratory, and time.
3.1.6 precision, n—the closeness of agreement between
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This practice is under the jurisdiction ofASTM Committee E11 on Quality and
independent test results obtained under stipulated conditions.
Statistics and is the direct responsibility of Subcommittee E11.20 on Test Method
3.1.6.1 Discussion—Precision depends on random errors
Evaluation and Quality Control.
and does not relate to the accepted reference value.
Current edition approved Nov. 15, 2006. Published January 2007. Originally
approved in 1961. Last previous edition approved in 2006 as E 177 – 06a.
3.1.6.2 Discussion—The measure of precision usually is
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or
expressed in terms of imprecision and computed as a standard
contact ASTM Customer
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