A new approach to the assessment of stochastic errors of radio source
  position catalogues
  Assessing the external stochastic errors of radio source position catalogues
derived from VLBI observations is important for tasks such as estimating the
quality of the catalogues and their weighting during combination. One of the
widely used methods to estimate these errors is the three-cornered-hat
technique, which can be extended to the N-cornered-hat technique. A critical
point of this method is how to properly account for the correlations between
the compared catalogues. We present a new approach to solving this problem that
is suitable for simultaneous investigations of several catalogues. To compute
the correlation between two catalogues $A$ and $B$, the differences between
these catalogues and a third arbitrary catalogue $C$ are computed. Then the
correlation between these differences is considered as an estimate of the
correlation between catalogues $A$ and $B$. The average value of these
estimates over all catalogues $C$ is taken as a final estimate of the target
correlation. In this way, an exhaustive search of all possible combinations
allows one to compute the paired correlations between all catalogues. As an
additional refinement of the method, we introduce the concept of weighted
correlation coefficient. This technique was applied to nine recently published
radio source position catalogues. We found large systematic differences between
catalogues, that significantly impact determination of their stochastic errors.
Finally, we estimated the stochastic errors of the nine catalogues.
