Tests for superclustering of Abell Cluster

Abell's catalog of rich clusters of galaxies has been examined for evidence of second-order clustering in three dimensions. Although the serial correlation coefficient by itself implies that superclustering exists, we do not interpret this result as evidence for superclustering. Instead, we have carried out further tests in order to show that systematic errors in the catalog are most probably the reasons why the serial correlation coefficient is large. The two-dimensional distribution of clusters on the sky has also been reanalyzed with the x1 test in order to examine the angular scale of apparent superclustering as a function of distance. `e find no correlation with distance. In order to study the influence of selection effects on the distribution of clusters and in order to see whether superclustering is evident by visual inspection, we have generated a stereoscopic pair of threedimensional perspective plots of Abell's catalog. The influence of apparent digit preferences is plainly visible as concentric shells of clusters of galaxies. Our results cannot be interpreted as evidence against superclustering. The results do, however, call into question the use of several statistical tests on data which are influenced by selection effects.