Error and Uncertainty in Physical Measurements

Abstract

‘Error’ and ‘uncertainty’ are two complementary, but distinct, aspects of the characterization of measurements. ‘Error’ is the difference between a measurement result and the value of the measurand while ‘uncertainty’ describes the reliability of the assertion that the stated measurement result represents the value of the measurand. The analysis of error considers the variability of the results when the measurement process is repeated. The evaluation of uncertainty considers the observed data to be given quantities from which the estimates of certain parameters (the measurement results) are to be deduced. The failure to distinguish between these two concepts has led to inconsistency, and a lack of uniformity in the way uncertainties have been expressed. The 1993 ISO (International Organization for Standardization) Guide to the Expression of Uncertainty in Measurements is the first international attempt to establish this uniformity and makes no distinction in the treatment of contributions to the total uncertainty in a measurement result between those arising from “random errors” and those arising from “systematic errors.”