Normal probability plots of the right ascension (left) and declination (right) optical-radio coordinate differences. The data are normally distributed because the graphs approximately coincide with the 45° reference line. There are considerably more objects at both ends of the ordered sample data, however, which indicates a heavy tail in the distribution. The curves surrounding the quantile points indicate the 95% confidence interval. The quantiles of the sample data are normalized to the same length reference distribution of N(0,1).