Practical Software for Automatic Uncertainty Propagation

K.D. McCroan1 and C.V. Gogolak2 (1EPA National Air and Radiation Environmental Laboratory; 2DHS Environmental Measurements Laboratory)

The need for good uncertainty analysis in the laboratory is commonly recognized, but because of the mathematical complexity of uncertainty propagation, laboratories sometimes do partial uncertainty evaluations involving only a few of the most easily determined components, such as the counting uncertainty. Even the partial uncertainty evaluations are sometimes done incorrectly. At the 49th annual meeting of the HPS, a paper was presented that described a conceptual approach to automatic uncertainty propagation using object-oriented software, and an implementation of the concepts in a Windows DLL. Since that time the same concepts have been used to create a user-friendly Windows application that allows any user to create a mathematical model of a measurement, enter data with numerical values, units, and uncertainties, and to calculate measurement results with propagated uncertainties as well as propagated physical dimensions. The program includes a library of mathematical functions, certain pre-defined mathematical and physical constants, and a database of nuclides with half-lives and relative atomic masses. The program offers formatting options for results and uncertainties, and expresses results in units specified by the user. Dimensional errors, such as the addition of two quantities of different dimensions or attempting to express results in units with the wrong dimensions, are detected automatically. The application allows a user to define and update mathematical models of measurement, define new measurement units, and calculate results interactively. It also provides the capability to open a previously defined model and a comma-separated text file of imported data, and run the model on each data set in the file. The program generates a printout for each data set showing the calculated results. The application is offered to the laboratory community as freeware.

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