  The APM Cluster Survey was based on a modification of Abell's original
classification scheme for galaxy clusters. Here we discuss the results of an
investigation of the stability of the statistical properties of the cluster
catalogue to changes in the selection parameters. For a poor choice of
selection parameters we find clear indications of line-of-sight clusters, but
there is a wide range of input parameters for which the statistical properties
of the catalogue are stable. We conclude that clusters selected in this way are
indeed useful as tracers of large-scale structure.
