Understanding ASTM C670: Precision and Bias in Construction Materials Testing

ASTM C670 Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials 

ASTM C670 Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials requires that all ASTM test methods contain statements on precision and bias. Each individual standard includes a statement on single-operator precision (repeatability) and a statement on multilaboratory precision (reproducibility).

Single-Operator Precision (Repeatability) of ASTM Test Methods 

It is well understood by engineers, scientists and technical people that there is some level of variability between tests when a single operator performs the same test repeatedly with the same piece of equipment. This variability is called the “repeatability” of a test method.

Multilaboratory Precision (Reproducibility) of ASTM Test Methods 

We also understand that if that same test is performed (even within the strict guidelines of an ASTM test method on sophisticated equipment) by a different operator on another plaice of equipment, there will likely by a higher level of variability. This variability is called the “reproducibility” of a test method.

The Role of Interlaboratory Studies in ASTM C670 Precision and Bias Statements 

ASTM has what they call an Interlaboratory Study Program which determines the precision and bias of each test method. The precision and bias can then be used to calculate the repeatability and reproducibility of the test method. Comprehensive interlaboratory studies are a key component in the development of precision and bias statements.

Components of a Research Report According to ASTM C670 

When an interlaboratory study is completed, the details are documented in a comprehensive research report. Per Section A29.1 of the ASTM Form and Style Manual, research reports are a requirement when numerical data is used to establish the precision and bias of a test method. Research Reports must include:

• List of participating laboratories
•  Description of samples tested
•  Copy of the laboratory instructions
•  Equipment/apparatus used
•  Copy of the raw data
•  Statistical summary
•  Copy of the precision and bias statement

Addressing Misconceptions and Variability in Test Methods with ASTM C670 

There is a lot of inaccurate information being spread about the precision and bias of ASTM test methods but the truth is, some of the equipment and test methods used have a high degree of variability. ASTM understands this and no ASTM test method that returns a single numerical value can be published without an extensive interlaboratory study, and the development of precision and bias statements based on this study.

Why ASTM C670 Emphasizes Precision and Bias in Test Results 

Those that understand probability and statistics understand that no matter how tightly controlled a test is, there is a natural variability in the results. The only way you can accurately normalize data and compare results is to understand the precision and bias inherent in the test method and develop confidence intervals for comparison.

Navigating ASTM C670 with Help from Sherwin-Williams

Navigating the complexities of ASTM C670, particularly when it comes to precision and bias in test methods for coatings, can be challenging. When comparing test results from different coating manufacturers, you must consider the reproducibility statement (multilaboratory precision) criteria. If the required result of the ASTM test is 100 and the multilaboratory coefficient of variation for that test method was found to be 20%, then a result of 80 is statistically equivalent. This is why it’s important to understand the specific requirements of each standard that are included in your specifications.

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ASTM C670 FAQs 

What is ASTM C670? 

ASTM C670 is a standard practice that provides guidelines for preparing precision and bias statements in test methods used for construction materials. These statements help in understanding the accuracy and reliability of test results.

Why is precision and bias important in ASTM test methods? 

Precision and bias are crucial because they help quantify the variability and reliability of test results to ensure that test methods provide accurate and consistent data.

What industries follow ASTM C670?

Industries involved in construction materials testing, such as building materials, civil engineering and infrastructure, are required to follow ASTM C670 to ensure the precision and accuracy of test methods. This standard is important for sectors like manufacturing, water management and environmental testing to maintain quality and compliance in their materials.

What is the difference between single-operator precision and multilaboratory precision in ASTM C670?

Single-operator precision (repeatability) refers to the consistency of test results when performed by the same operator, while multilaboratory precision (reproducibility) measures the consistency of results when the test is conducted by different operators in different laboratories.