Estimation of measurement uncertainty in chemical analysis
3.3. A and B type uncertainty estimates
Carrying out the same measurement operation many times and calculating the standard deviation of the obtained values is one of the most common practices in measurement uncertainty estimation. Either the full measurement or only some parts of it can be repeated. In both cases useful information can be obtained. The obtained standard deviation (or the standard deviation of the mean, explained in section 3.4) is then the standard uncertainty estimate. Uncertainty estimates obtained as standard deviations of repeated measurement results are called A type uncertainty estimates. If uncertainty is estimated using some means other than statistical treatment of repeated measurement results then the obtained estimates are called B type uncertainty estimates. The other means can be e.g. certificates of reference materials, specifications or manuals of instruments, estimates based on long-term experience, etc.
