5.1 ASTM regulations require precision statements in all test methods in terms of repeatability and reproducibility. This practice may be used in obtaining the needed information as simply as possible. This information may then be used to prepare a precision statement in accordance with Practice E177.
5.2 Test Method and Protocol—In this practice, the term “test method” is used both for the actual measurement process and for the written description of the process, while the term “protocol” is used for the directions given to the laboratories for conducting the ILS.
5.3 Observations, Test Determinations and Test Results:
5.3.1 A test method often has three distinct stages, the direct observation of dimensions or properties, the arithmetic combination of the observed values to obtain a test determination, and the arithmetic combination of a number of test determinations to obtain the test result of the test method. In the simplest of test methods a single direct observation is both the test determination and the test result. For example, the test method may require the measurement of the mass of a test specimen prepared in a prescribed way. Another test method may require the measurement of the area of the test specimen as well as the mass, and then direct that the mass be divided by the area to obtain the mass per unit area of the specimen. The whole process of measuring the mass and the area and calculating the mass per unit area is a test determination. If the test method specifies that only one test determination is to be made, then the test determination value is the test result of the test method. Some test methods require that several determinations be made and the values obtained be averaged or otherwise combined to obtain the test result of the test method. Averaging of several determinations is often used to reduce the effect of local variations of the property within the material.
5.3.2 In this practice, the term “test determination” is used both for the process and for the value obtained by the process, except when “test determination value” is needed for clarity.
5.3.3 The number of test determinations required for a test result should be specified in each individual test method. The number of test results required for an interlaboratory study of a test method is specified in the protocol of that study.
5.4 Test Specimens and Test Units—In this practice a test unit is the total quantity of material needed for obtaining a test result as specified by the test method. The portion of the test unit needed for obtaining a single test determination is called a test specimen. Usually a separate test specimen is required for each test determination.
5.5 Precision, Bias, and Accuracy of a Test Method:
5.5.1 When a test method is applied to a large number of portions of a material, that are as nearly alike as possible, the test results obtained nevertheless will not all have the same value. A measure of the degree of agreement among these test results describes the precision of the test method for that material.
5.5.2 Numerical measures of the variability between such test results provide inverse measures of the precision of the test method. Greater variability implies smalle......