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The purpose of this practice is to present concepts necessary to the understanding of the terms “precision” and “bias” as used in quantitative test methods. This practice also describes methods of expressing precision and bias and, in a final section, gives examples of how statements on precision and bias may be written for ASTM test methods. A statement of precision allows potential users of a test method to assess in general terms the test method’s usefulness with respect to variability in proposed applications.
This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.
Significance and Use
4.1 Part A of the “Blue Book,” Form and Style for ASTM Standards, requires that all test methods include statements of precision and bias. This practice discusses these two concepts and provides guidance for their use in statements about test methods.
4.2 Precision—A statement of precision allows potential users of a test method to assess in general terms the test method’s usefulness with respect to variability in proposed applications. A statement of precision is not intended to exhibit values that can be exactly duplicated in every user’s laboratory. Instead, the statement provides guidelines as to the magnitude of variability that can be expected between test results when the method is used in one, or in two or more, reasonably competent laboratories. For a discussion of precision, see .
4.3 Bias—A statement of bias furnishes guidelines on the relationship between a set of typical test results produced by the test method under specific test conditions and a related set of accepted reference values (see ).
4.3.1 An alternative term for bias is trueness, which has a positive connotation, in that greater bias is associated with less favorable trueness. Trueness is the systematic component of accuracy.
4.4 Accuracy—The term “accuracy,” used in earlier editions of Practice , embraces both precision and bias (see ).
1.1 The purpose of this practice is to present concepts necessary to the understanding of the terms “precision” and “bias” as used in quantitative test methods. This practice also describes methods of expressing precision and bias and, in a final section, gives examples of how statements on precision and bias may be written for ASTM test methods.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E1488 Guide for Statistical Procedures to Use in Developing and Applying Test Methods
E2282 Guide for Defining the Test Result of a Test Method
E2586 Practice for Calculating and Using Basic Statistics
E2587 Practice for Use of Control Charts in Statistical Process Control
ICS Number Code 19.020 (Test conditions and procedures in general)
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ASTM E177-20, Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods, ASTM International, West Conshohocken, PA, 2020, www.astm.orgBack to Top