Labsinus >
ASTM E691 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
Last updated August 27, 2025
ASTM E691 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
It is crucial to the validity of any industrial or scientific test procedure that it be precise and reproducible. The purpose of the ASTM E691 is to give a systematic method of carrying out an interlaboratory study (ILS) to assess the precision of a standardized method of test. The method is concerned with repeatability, the measure of variability between tests conducted by the same operator on the same equipment, and reproducibility, which is the difference when tests are run between different labs. By producing statistically sound data, ASTM E691 enhances the credibility of test procedures and substantiates their introduction into industry, regulatory settings, and research. It provides standardization of test results in varying laboratory settings.
Read More
GET STARTED
ASTM E691 Introduction
ASTM E691 aims to standardise the process of comparison test methods by coordinating several laboratories to carry out the same test under set conditions. This is crucial to the practice of ensuring that methodologies are not only sound with respect to technical merit but also provide results that compare in diverse contexts. An interlaboratory study requires planning, execution, and statistical analysis of test results to find out sources of variation. The final objective is to quantify the precision limits of a test method, which are required for inclusion in ASTM and other consensus standards. These types of studies enhance confidence in test data, improve method reliability, and establish benchmarks for global acceptance.
ASTM E691 Test Method
Study Design
A typical selection of six laboratories and various test materials is chosen to provide a sufficient level of data coverage.
Testing of the materials
All laboratories conduct tests on supplied materials according to the specified test method without reducing the scope.
Data Gathering
Data are strategically compiled to facilitate statistical analysis.
Statistical Evaluation
The limits of repeatability and reproducibility are obtained by analysis of variance (ANOVA) and other statistical methods.
ASTM E691 Sample Preparation and Equipment
Sample Selection
Representative Samples of the test material are selected in order to depict the intention of the scope of the method. Material specifications should be consistent so as to make valid comparisons.
Sample Distribution
To minimize variability caused by material differences, the same samples are prepared and then distributed to the participating laboratories.
Equipment requirements
The equipment required in labs (must comply with the standard method requirements) must be calibrated prior to use to ensure comparability of data.
ASTM E691 Results and Interpretation
An ASTM E691 study provides its results in the form of repeatability (r) and reproducibility (R) limits. Repeatability refers to the amount of variation that would be expected when the same test is run in the same laboratory, whereas reproducibility refers to the variation between laboratories. Statistical analysis demonstrates consistency in the results obtained from the test procedure when performed under various conditions. The narrower the range of r values and R values, the greater the precision and reliability of that method; wider ranges may imply the need to calibrate procedures, provide operator training, or adjust equipment.
Several standards, including ASTM E691, complete the precision and validation of methods. Greater precision and bias key terms related to testing methods are identified in ASTM E177. The ASTM E29 sets out rounding significant figures in the reporting of test results. ISO 5725 also provides international guidance on the terms and definitions of accuracy, precision, and trueness of test methods. In combination, the standards constitute a coherent system of creating and demonstrating statistically valid test procedures that can be used internationally to harmonize testing procedures.
ASTM E691 Application in Industry
In industries where it is important to test by a standard method, ASTM E691 plays an important role. In material testing, it confirms procedures for mechanical, chemical, and thermal properties. In pharmaceuticals and biotechnology, it facilitates accurate evaluation of analytical processes and helps with regulatory adherence. ASTM E691 is used by environmental testing laboratories in establishing the compatibility of their monitoring networks. It has numerous applications in food science, construction, and energy sectors to provide confidence in test results. ASTM E691 also allows industries to introduce a high-quality assurance program and global acceptance of standard testing procedures by providing an overall structure for precision evaluation.