Published by the American Society for Testing and Materials (ASTM), the ASTM E177-19 standard provides the necessary concepts for understanding the terms of precision and deviation used in quantitative testing methods. This standard also describes methods for expressing certainty and bias, and in the last section gives examples of how statements about precision and bias can be written for ASTM test methods. The full name of this standard is as follows: ASTM E177-19 Standard practice for the use of the terms precision and deviation in ASTM test methods.
Statement of precision allows users applying a test method to evaluate with general statements how useful the test method is in terms of variability in the proposed applications. The statement of precision is not intended to show values that can be accurately reproduced in the laboratory for every user. Instead, the method provides instructions on the extent of variation that can be expected between test results when used in one or two or more reasonably competent laboratories.
The ASTM E177-19 standard takes into account quantitative test methods that produce only numerical results. For example, the concept of material is used in the sense of material, product, system or service. The concept of property means that a quantitative test result can be obtained that describes a property or quality or other aspect of the material. Test method statement refers to both the document and the procedure described here to obtain a quantitative test result on a property.
A deviation statement provides guidelines on the relationship between accepted reference values for a set of typical test results produced by the test method under certain test conditions.
An alternative term for bias is truth, truth. This concept has a positive connotation as more bias is associated with less appropriate reality. Accuracy is a systematic component of precision. Truth statement includes both precision and bias.
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