ASTM E691 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

Get Certified ASTM E691 Testing for Reliable Test Method Precision Data 

Certification verify the precision statement for a test method meets the applicable ASTM E691 requirements, including adequate calculation of the repeatability and reproducibility values from the appropriate interlaboratory study. The ASTM E691-certified analysis compares the precision data from a test method to those of similar methods before a standards committee adopts it as the basis for a published precision statement. Testing and certification establish conformance with ASTM E691 requirements and minimize the potential for unsupported precision claims. 

The primary purpose of ASTM E691 is to determine the repeatability and reproducibility of a test method by conducting a coordinated study of the method in multiple laboratories. This practice is used in industries for test method validation, development of standards, and quality assurance benchmarking.

• Material type: Homogeneous test materials or products that are representative of the use of the test method. 
• Purpose: To measure and evaluate a test method’s repeatability and reproducibility. 
• Properties evaluated: Ability to obtain the same test result on the same material from different laboratories. 
• Testing Method: Laboratories share equal amounts of material. Each lab produces duplicate test results with the same test method. 
• Result: Analysts report precision as repeatability and reproducibility standard deviations, formatted per ASTM E177. 
• Test Limitations: The practice only estimates test method precision; it does not confirm that an individual laboratory has in-control operating conditions over time. 
• Use conditions: Measured reproducibility depends directly on the operator, the equipment, the calibration, and the differences between the various laboratories. 
• Applications: Test method validation for new ASTM standards, precision statement development, standards committee round-robin studies, quality assurance benchmarking. 

What are the Uses of ASTM E691 Testing?

ASTM E691 testing helps in the development of a precision study of a test method by the standards committee and by multiple laboratories. The analysts use the test results to check test data against specification limits and to assess the consistency between laboratories. This standard-

• Evaluates the reproducibility of a test method in one lab.
• Reproduces the same material in several laboratories and measures reproducibility.
• Uses tabular, graphical, and statistical diagnostic tools to evaluate the consistency of test data.
• Helps develop a formal precision statement to ASTM E177.
• Helps identify abnormal or unusual laboratory values.
• Helps validate test methods and develop standards.
• Helps to select appropriate test methods for a desired level of precision.

What Materials Can Be Tested Under ASTM E691? 

ASTM E691 is applicable to any test method that requires a statement of precision and applies to a test material or product that is homogeneous and represents the method’s intended application. Typical studies use multiple materials, or material levels, that analysts choose to represent the range of behavior a test method encounters in practice. Analysts choose laboratories that use the test method in normal operational conditions and designate participants covering a range of abilities. 

Why is ASTM E691 Important? 

ASTM E691 provides a consistent statistical practice for determining the repeatability and reproducibility of a test method. Standards committees employ this practice to meet the ASTM requirement that all published test methods include a precision statement containing documentation of the repeatability and reproducibility of the test method. 

ASTM E691 Testing Process and Data Collection

Testing begins with the design of the interlaboratory study and the number of laboratories, materials, and replicate determinations required. Analysts then prepare an identical set of sample volumes for each test material and send them to the participating laboratories, along with the test protocol. Each laboratory conducts the test with its own set of specimens and under its own standard operating conditions, and reports back to the study coordinator. The coordinator combines data from all the laboratories into a single set. Lastly, the analysts use tabular, graphical, and statistical diagnostic tools for this data and compute the repeatability and reproducibility, as well as recognize unusual values that might need additional investigation. 

Common Challenges and Troubleshooting

A lack of specimen homogeneity is often a source of error that leads to an overestimate of precision, since material variation between laboratories mimics genuine test method variability. When analysts eliminate outlier data without understanding the issue, there may also be misleading information about the actual sources of variance. Failing to have a representative selection of laboratories participate results in a precision statement that is not representative of real-world testing situations. Analysts address these concerns who check for material homogeneity prior to distribution, not automatically rejecting unusual results, and involving a representative subset of the laboratories that participate. 

• The laboratory reports the standard deviation for repeatability and reproducibility of the test, in accordance with ASTM E177.
• The technician specifies the test method and materials examined, the number of laboratories, and replicate determinations.
• Analysts enter the consistency statistics obtained from the data and make a correlation with the tested materials and the laboratory.
• The engineer takes the precision result and interprets it based on the following parameters: Homogeneity of the material, Laboratory participation range, and Outlier investigation.
• Engineers use the calculated repeatability and reproducibility values to support test method validation and standards development decisions. 

Link to ASTM E691