ASTM E691-23 PDF

Overview

ASTM E691-23 – Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method provides detailed guidance for planning, executing, and analyzing an interlaboratory study (ILS) to evaluate the precision of a test method. Precision statements, including repeatability and reproducibility, are essential in ASTM test methods. This practice is designed for test methods that deliver a single numerical value, though that value may come from calculations involving multiple measurements. The primary aim is to facilitate the generation of statistically valid precision data, which is critical for comparing test results and supporting quality control across laboratories.

Key Topics

• Interlaboratory Study (ILS) Design: Guidance on assembling an ILS task group, selecting participating laboratories, and choosing test materials. Emphasizes the importance of a clear protocol and a well-developed, validated test method.
• Precision Metrics: Directions for determining repeatability (within-laboratory variability) and reproducibility (between-laboratory variability). Precision can be expressed through standard deviation, coefficient of variation, or precision limits.
• Phases of ILS:
  • Planning: Establishing study aims, experimental design, and participant responsibilities.
  • Testing: Coordinating material distribution, following protocol, and collecting data.
  • Analysis: Applying statistical tools to interpret data and identify outliers, followed by the calculation of numerical measures of test method precision.
• Protocol Development: Importance of specifying calibration, material handling, data recording, and reporting procedures.
• Data Consistency: Procedures for identifying and investigating inconsistent results, including guidelines for dealing with unexpected data and refining methods as needed.
• Participants’ Roles: Assigns responsibilities, including ILS coordinator, data analyst, laboratory supervisors, and statistician, to ensure study validity.

Applications

• Quality Control: Laboratories use this standard to assess and compare test method precision, critical for regulatory compliance and internal quality assurance.
• Method Validation: Provides a framework for validating the precision of existing test methods before widespread adoption in industry or research.
• Commercial and Technical Decision-Making: Enables organizations to objectively evaluate whether a test method is suitable for purpose, especially when precise comparison to specifications or between sources is required.
• Regulatory Compliance: Many sectors, including pharmaceuticals, environmental testing, and materials science, require ASTM-compliant precision statements as part of method documentation.
• Test Method Improvement: Results from ILS may reveal the need for method refinement when high variability or bias is detected.

Related Standards

• ASTM E177 - Practice for Use of the Terms Precision and Bias in ASTM Test Methods: Establishes terminology and criteria for method precision and bias.
• ASTM E29 - Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications: Guides proper reporting of numerical data.
• ASTM E456 - Terminology Relating to Quality and Statistics: Offers definitions for key statistical quality terms.
• ASTM E1169 - Practice for Conducting Ruggedness Tests: Helps identify critical variables in test methods.
• ASTM E1402 - Guide for Sampling Design: Covers principles for representative sample selection in test design.
• ASTM E2282 - Guide for Defining the Test Result of a Test Method: Provides further direction on reporting test results.

Conclusion

ASTM E691-23 is an invaluable resource for any organization seeking to ensure the statistical validity and comparability of quantitative test methods through robust interlaboratory studies. Proper application of this practice enhances confidence in reported results, compliance with international standards, and the credibility of laboratory testing within and between organizations. For maximum benefit, users should refer to this standard in conjunction with related ASTM practices and guides.