Measurement Uncertainty - GUM Approach

GUM Approach

The Guide to the Expression of Uncertainty in Measurement (GUM) is a document published by the JCGM that establishes general rules for evaluating and expressing uncertainty in measurement.

The GUM provides a way to express the perceived quality of the result of a measurement. Rather than express the result by providing an estimate of the measurand along with information about systematic and random error values (in the form of an "error analysis"), the GUM approach is to express the result of a measurement as an estimate of the measurand along with an associated measurement uncertainty.

One of the basic premises of the GUM approach is that it is possible to characterize the quality of a measurement by accounting for both systematic and random errors on a comparable footing, and a method is provided for doing that. This method refines the information previously provided in an "error analysis", and puts it on a probabilistic basis through the concept of measurement uncertainty.

Another basic premise of the GUM approach is that it is not possible to state how well the true value of the measurand is known, but only how well it is believed to be known. Measurement uncertainty can therefore be described as a measure of how well one believes one knows the true value of the measurand. This uncertainty reflects the incomplete knowledge of the measurand.

The notion of "belief" is an important one, since it moves metrology into a realm where results of measurement need to be considered and quantified in terms of probabilities that express degrees of belief.