ASTM E177-04

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An American National Standard
Designation:E177–04
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.
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 1169 Guide for Conducting Ruggedness Tests
within a laboratory for the same operator.”
2.2 Other Document:
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3.1.4.2 Discussion—Because the training of operators, the
ISO 3534 Statistics—Vocabulary and Symbols
agreement of different pieces of equipment in the same
3. Terminology
laboratory and the variation of environmental conditions with
longer time intervals all depend on the degree of within-
3.1 Definitions:
laboratory control, the intermediate measures of precision are
3.1.1 accepted reference value, n—a value that serves as an
likely to vary appreciably from laboratory to laboratory. Thus,
agreed-upon reference for comparison, and which is derived
intermediate precisions may be more characteristic of indi-
as: (1) a theoretical or established value, based on scientific
vidual laboratories than of the test method.
principles, (2) an assigned or certified value, based on experi-
3.1.5 intermediate precision conditions, n—conditions un-
mental work of some national or international organization, or
der which test results are obtained with the same test method
(3) a consensus or certified value, based on collaborative
using test units or test specimens (10.3) taken at random from
experimental work under the auspices of a scientific or
a single quantity of material that is as nearly homogeneous as
engineering group.
possible, and with changing conditions such as operator,
measuring equipment, location within the laboratory, and time.
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This practice is under the jurisdiction ofASTM Committee E11 on Quality and
3.1.6 precision, n—the closeness of agreement between
Statistics and is the direct responsibility of Subcommittee E11.20 on Test Method
independent test results obtained under stipulated conditions.
Evaluation and Quality Control.
3.1.6.1 Discussion—Precision depends on random errors
Current edition approved Nov. 1, 2004. Published December 2004. Originally
approved in 1961. Last previous edition approved in 2002 as E 177 – 90a (2002). and does not relate to the accepted reference value.
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
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