ASTM E177-20 PDF

Full title and description

ASTM E177-20 — Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods. This practice defines and explains the statistical concepts of precision and bias (trueness) as applied to quantitative ASTM test methods, and provides guidance and examples for writing precision and bias statements in test methods.

Abstract

The practice presents the concepts needed to understand the terms "precision" and "bias" for test methods that yield numerical results. It describes how precision and bias can be expressed, discusses sources of variability (repeatability, reproducibility and other contributors), and gives example statements and preferred indexes to be used when including precision and bias information in ASTM test methods.

General information

• Status: Active (current version)
• Publication date: October 1, 2020 (E177-20); last updated October 16, 2020
• Publisher: ASTM International
• ICS / categories: ICS 19.020 (test conditions and procedures / statistical methods and quality/statistics)
• Edition / version: E177-20 (2020)
• Number of pages: 10

Scope

This practice is intended for quantitative test methods that produce numerical results. It explains the terms precision and bias, describes preferred ways to express them (indexes and statement formats), addresses how precision and bias vary with materials and sources of variability, and provides examples of precision and bias statements suitable for inclusion in ASTM test methods. It does not prescribe safety practices; users are responsible for applicable safety and regulatory considerations.

Key topics and requirements

• Definitions and discussion of key measurement terms: precision, bias (trueness), accuracy, repeatability, reproducibility.
• Identification and description of sources of variability (operator, apparatus, environment, sample, time, etc.).
• Preferred statistical indexes for expressing precision (standard deviation, coefficient of variation, precision limits) and guidance on bias statements.
• Guidance on combining sources of variability and on distinguishing within-lab and between-lab measures.
• Examples and model wordings for precision and bias statements to be used in test methods.
• Guidance on the interpretation and practical use of precision and bias values when comparing results or assessing method suitability.

Typical use and users

Used by standards writers, test method developers, laboratory quality managers, statistical analysts, accreditation bodies, and organizations that run interlaboratory studies. Typical applications include preparing or reviewing precision/bias statements in test methods, planning interlaboratory studies, interpreting method variability for specifications and decision limits, and training personnel on measurement uncertainty concepts.

Related standards

Commonly used alongside ASTM practices and international standards that address interlaboratory studies and accuracy of measurement, including ASTM E691 (Interlaboratory study practice for estimating precision) and the ISO 5725 series (accuracy — trueness and precision). Other related ASTM guidance and practices (for example those addressing measurement technology, equivalence testing, or specific test-method precision procedures) are often used in support of statements recommended by E177.

Keywords

precision, bias, trueness, accuracy, repeatability, reproducibility, interlaboratory study, statistical control, accepted reference value, precision statement, measurement variability

FAQ

Q: What is this standard?

A: ASTM E177-20 is a practice that defines and explains the terms precision and bias (trueness) and gives guidance on expressing and reporting these quantities in quantitative ASTM test methods.

Q: What does it cover?

A: It covers conceptual definitions, sources of variability, preferred statistical indexes and formats for precision and bias statements, examples of statement wording, and how to interpret precision and bias when applying test methods and comparing results.

Q: Who typically uses it?

A: Standards authors, laboratory managers, statisticians, accreditation assessors, and anyone involved in drafting, validating, or using quantitative test methods that require precision and bias information.

Q: Is it current or superseded?

A: E177-20 is the active version published in 2020 and remained current as the active ASTM practice. (A committee work item to revise E177 was recorded in 2025; users should check the ASTM document status pages for any formal revision or replacement after 2025.)

Q: Is it part of a series?

A: E177 is a standalone ASTM practice within the E11 committee portfolio but is commonly used together with related standards such as ASTM E691 (interlaboratory study practice) and the ISO 5725 series on accuracy (trueness and precision).

Q: What are the key keywords?

A: Precision, bias (trueness), repeatability, reproducibility, accuracy, interlaboratory study, statistical control, accepted reference value.