“Testing” is a term that covers a vast range of activities. Not every test is a measurement; some are visual inspections or can be qualified with nominal descriptions such as “pass or fail” or “hot or cold”. However, for tests that either are measurements or include measurements, understanding the uncertainty of those measurements is important to interpreting resulting data. An important component of test method validation is an uncertainty analysis that systematically assesses the factors influencing the measurement.
Instruments and the process of calibration to reference standards are not perfect. Neither is the person performing the test, the environment, or the test method itself. Therefore, every measurement has some uncertainty associated with it. The use of recognized standard procedures reduces many potential sources of measurement uncertainty, however even when the method is standardized, the uncertainty of the method should be understood.
A measurement is a function of all the input quantities that affect the measurement. For example, for the measurement of volume there might be three measurements (length, width, height). The uncertainty in the volume measurement can be determined by calculating and combining each measurement uncertainty along with the uncertainty associated with other factors (e.g., temperature or hydration).
Measurement uncertainty is a statistical estimate of experimental error. Thus, when estimating the uncertainty of a measurement, uncertainty components which are of importance in the given situation should be taken into account using appropriate statistics.
When a test method validation includes an uncertainty analysis to systematically assess the factors influencing the measurement, use of the test method for inappropriate applications can be avoided. The test method may also be improved, controlled, or monitored in areas of high uncertainty, ultimately building more confidence into the associated results.
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