Estimation of measurement uncertainty in physical analysis laboratory
Pages 112-117
I. Piciorea
Abstract. Many decisions, in all fields of human activities, are based on the results of measurements. Therefore it is essential that such results are reliable. This can be achieved by, among other things, establishing traceability of the results to stated references and providing an estimate of the uncertainty of measurement based on an uncertainty budget including all known uncertainty contributions. In analytical chemistry several sources contribute to the deviation of an individual result from an unknown “true” value. These are sometimes indicated from a laboratory point of view as a ladder of errors including the measurement procedure (method) bias, the lab bias, the run error and the repeatability error. Consistent treatment of measurement bias, including the question of whether or not to correct for bias, is essential for the comparability of measurement results. Several different published approaches to the treatment of uncorrected bias and its uncertainty are critically reviewed with regard to coverage probability and simplicity of execution.
The fundamental document on expression of uncertainty in measurement, the ISO/IEC Guide to the Expression of Uncertainty measurement [1] (GUM), was published in 1993 following the collaborative effort of metrological organization, standardization bodies and scientific societies involved in the science of measurement. The principles of the GUM are recognized to apply to all types of quantitative measurements, in all field of application. A prerequisite for the application of the GUM is that “the result of a measurement has been corrected for all recognized significant systematic effects” (GUM 3.2.4). This implies that when developing a measurement procedure all possible sources of bias should be investigated and if deemed appropriate a correction should be incorporated into the procedure.