Information-based probability density function for a quantity

The modem approach to the evaluation of measurement data in metrology is based on the mathematical formulation of the simple idea that any kind of information that is relevant for inferencing the measurand generates a corresponding state of knowledge about the measurand. This paper briefly discusses the basic concept of probability density function (pdf), which is the mathematical description of the state of knowledge about the measurand corresponding to given information. Two ways to establish a pdf are described. The recommendations for data evaluation in the Guide to the Expression of Uncertainty in Measurement [1] rest on this concept.