CPB Ljubljana 2018 course book

Definition of Uncertainty: Types of Uncertainty

Uncertainty is a parameter that characterizes the dispersion of values that can be obtained for a particular measurement when it is performed repeatedly. For such repeated measurements, the results can be represented by a statistical distribution, which can be summarized by specific statistical quantities such as mean, mode, standard deviation, and variance .

Standard uncertainty is the standard deviation. The symbol often attributed to the standard uncertainty is u .

Combined standard uncertainty is the standard uncertainty of a quantity that is composed of various components, each of which has its own uncertainty. The combined standard uncertainty is obtained by summing up the square of the individual standard deviations and taking the square root. This assumes a gaussian distribution for each of the contributing uncertainties. This mathematical procedure for combining uncertainties is generally known as “addition in quadrature” or error propagation.

Accuracy and Uncertainty Considerations in Modern Radiation Oncology, The Modern Technology of Radiation Oncology, J. Van Dyk, 2013