Data pooling and key comparison reference values

Key comparison data are often reported, as a matter of policy, with respect to a reference value calculated from the pool of the participants' results. Consideration of the comparison data sets, particularly with regard to the consequences and implications of such data pooling, can justify the choice of a simple statistical reference value. Recent key comparisons in thermometry are examined to illustrate the nature of the problem, and the utility of a simple approach to creating pooled data distributions. An objective criterion is introduced to help determine when a comparison can safely be described as a single population having a key comparison reference value (KCRV). Graphical techniques of data pooling are presented as an aid to harnessing expert opinion on this question.