Comparison of the sample correlation coefficients (circles) of the parallax errors of source pairs in Case A with the average theoretical coefficients (lines) computed for ω = 1.16 in successive approximations (α). The pairs were grouped in samples of equal size depending on θ, and the sample correlation coefficient plotted against the average θ of each group. To reduce the statistical uncertainty of the sample correlation coefficients (indicated by the error bars), many more pairs were used to compute the sample values than the 150 000 pairs for which theoretical values were available.