ASTM E691-18: Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method features techniques for planning, conducting, analyzing, and treating the results of the interlaboratory study (ILS) of a test method.
The universe was once nothing but unknowns and uncertainties. Fortunately, the society we live in today has been shaped for the better with the aid of quantifiable data acquired through testing methods. Numerous scientific disciplines depend on reliable data for assessing phenomena and processes in the pursuit of explaining the natural world.
Data is just as important for industry, in which laboratory methods can assure the effective performance or other specifications of a product or material. However, reference points are necessary for assuring the reliability of results. This level of quality is gained, in part, due to accuracy and precision.
While many use the two interchangeably, precision and accuracy describe two different attributes of data. According to ASTM E177-14: Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods, accuracy describes “the closeness of agreement between a test result and an accepted reference value,” while precision is “the closeness of agreement between independent test results obtained under stipulated conditions.”
In fact, the ASTM E177-14 standard supports almost all ASTM test methods, which are detailed in an assortment of ASTM International standards serving numerous industries. Overall, this practice discusses concepts necessary for understanding precision and bias, and it covers how statements for precision and bias should be written for ASTM test methods.
According to Section 2 of the Regulations Governing ASTM Technical Committees, “a precision and bias statement shall be reported at the end of a test method.” While ASTM E177-14 details a great deal of information for drafting this statement, ASTM E691-18 covers the statistical techniques for gathering the information needed for a test method precision statement. However, it does not concern itself with the development of test methods.
Precision is reported as a standard deviation, coefficient of variation, variance, or a precision limit. ASTM E691-18 offers information for the concepts of test method precision and the means of preparing an interlaboratory study (ILS), conducting the testing phase of the ILS, calculating and displaying statistics, and data consistency. This information is used for the precision statement.
Knowledge of a test method’s precision is useful in commerce and in technical work when comparing test results against standard values or between data sources. Therefore, the information accumulated via the techniques of ASTM E691-18 for a precision statement written under the guidance of ASTM E177-14 for any ASTM test method can help support the reliability of standard practices.
ASTM E691-18: Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method is available on the ANSI Webstore.