How many shades of grey are in conformity assessment due to measurement uncertainty?

Abstract

Abstract When a measured value of a property of a material or object differs from the upper or lower specification limit (actual or ‘true’ value) by the expanded measurement uncertainty or more, there is the clear decision on the material conformity or nonconformity - ‘white’ or ‘black’. In the interval from the measured value to the specification limit, covered by the expanded measurement uncertainty (‘grey zone’), risks of false decisions on conformity increase. Several kinds of the risks, named ‘shades of grey’, should be taken into account. For a multicomponent material there are four kinds of particular risks for each property value of the material (e.g. component concentration or content), and four kinds of total risks related to the material as a whole. Therefore, for n > 1 properties under control for the material conformity assessment one can distinguish 4(n +1) kinds of risks of false decisions – shades of grey.