Type B uncertainties

Occasionally, both these uncertainty components are denoted (i) as type A - and (ii) as type B uncertainties. 

Note that the categories relate only to how the estimate was obtained, and not to whether the uncertainty is due to a random or a systematic effect. Type A uncertainty estimates are, by definition, expressed as a standard deviation. Type B uncertainty estimates can take a number of different forms, and may need to be converted to a standard uncertainty prior to combination with other uncertainty estimates. This is discussed later in this section. 

Hoffman and Hammonds (1994) Type A uncertainty Type B uncertainty Uncertainty... 

Epistemic uncertainty The kind of uncertainty arising from imperfect knowledge. Epistemic uncertainty is also known as incertitnde, ignorance, subjective uncertainty. Type II or Type B uncertainty, redncible nncertainty, nonspeci-hcity and state-of-knowledge uncertainty. 

High value only on T rise with hydrogen present low value for hydrogen added at high T Type B uncertainty based on sensor manufacturer s documentation... 

Type A uncertainties (cr ), determined by the counting statistics, and type B uncertainties, based on a scientific judgment are clearly distinguished. Type B uncertainty (cr ) takes into account the uncertainty on the activity of the calibration sources certificates and the uncertainty on the volumetry employed during the preparation of solutions (5.55 %). The total relative uncertainty cr ) spread to 2a (in %) of the activity in Sr is defined in the following general form ... 

The uncertainties of the assigned values were then evaluated [7] on the basis of the estimation of the Type A and Type B uncertainty components, due to the possible errors originating principally from preparation as well as from the direct measurement (method included), as follows ... 

In the theory on uncertainty, a distinction between type A and B uncertainties is made. Type A uncertainties are frequency-based estimates of standard deviations (e.g, an SD of the imprecision). Type B uncertainties are uncertainty components for which frequency-based SDs are not available. Instead, the uncertainty is estimated by other approaches or by the opinion of experts. Finally the total uncertainty is derived from a combination of all sources of uncertainty. In this context, it is practical to operate with standard uncertainties (w t), which are equivalent to standard deviations. By multiplication of a standard uncertainty with a coverage factor (k), the uncertainty corresponding to a specified probability level is derived. For example, multiplication with a coverage factor of two yields a probability level of 95% given a normal distribution. When considering the total uncertainty of an analytical result obtained by a routine method, the preanalytical variation, method imprecision, random matrix-related interferences, and uncertainty related to calibration and bias corrections (traceability) should be taken into account. Expressing the uncertainty components as standard uncertainties, we have the general relation ... 

Some relations between the SD and nonnormal distributions may also be of relevance for uncertainty calculations (type B uncertainties) (Table 14-16). For example, if the uncertainty of a CRM value is given with some percentage, it may be understood as referring to a rectangular probability distribution. In relation to calibration of flasks, the triangular distribution is often assumed. 

The specific approach to evaluating the standard uncertainty u. of a Type B uncertainty will depend on the detailed model of the measurement process. The following are examples of steps that may be used ... 

Type A uncertainty is obtained by a set of observed frequency distribution probability density function that is exported Type B uncertainty... 

However, a new distinction has arisen - Type A and Type B uncertainties. Type A uncertainties are defined as those that have been determined by repeated measurements to assess the magnitude and distribution of the parameter. Type B uncertainties are those whose magnitude has been derived in any other manner. For example, the uncertainty on gamma-ray emission probability is... 

Masses (mdb, ms) The standard uncertainties of the weighings have been determined previously according to an accepted guideline (EURAMET, 2009) and amount to u(ms) = w(mdb) = 0.05 mg. This is a type B uncertainty with infinite degrees of freedom. 

---