4.1 Laboratories conducting routine testing have a continuing need to evaluate test result bias, to evaluate changes for improving the test process performance, or to validate the transfer of a test method to a new location or apparatus. In all situations it must be demonstrated that any bias or innovation will have negligible effect on test results for a characteristic of a material. This standard provides statistical methods to confirm that the mean test results from a testing process are equivalent to those from a reference standard or another testing process, where equivalence is defined as agreement within prescribed limits, termed equivalence limits.
4.1.1 The intra-laboratory applications in this practice include, but are not limited to, the following:
(1) Evaluating the bias of a test method with respect to a certified reference material,
(2) Evaluating bias due to a minor change in a test method procedure,
(3) Qualifying new instruments, apparatus, or operators in a laboratory, and
(4) Qualifying new sources of reagents or other materials used in the test procedure.
4.1.2 This practice also supports evaluating systematic differences in a method transfer from a developing laboratory to a receiving laboratory.
4.2 This practice currently deals only with the equivalence of population means. In this standard, a population refers to a hypothetical set of test results arising from a stable testing process that measures a characteristic of a single material.
Note 1: The equivalence concept can also apply to population parameters other than means, such as precision, stated as variances, standard deviations, or relative standard deviations (coefficients of variation), linearity, sensitivity, specificity, etc.
4.3 The data analysis for equivalence testing of population means in this practice uses a statistical methodology termed the “Two one-sided t-test” (TOST) procedure which shall be described in detail in this standard (see X1.1). The TOST procedure will be adapted to the type of objective and experiment design selected.
4.3.1 Historically, this procedure originated in the pharmaceutical industry for use in bioequivalence trials (1, 2),3 denoted as the Two One-Sided Test, and has since been adopted for other applications, particularly in testing and measurement applications (3, 4).
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