This is really interesting. It is going to take me a little while to digest that paper. But even if they are right about the cause, it shows that Arp was at least right about the probabilities and the need to investigate further.

One thing about the catalog that surprised me was the number of pairs that have both one quasar paired with many galaxies and one galaxy paired with many quasars. That requires some different statistical measures.

They had a cut-off of galaxy redshift at z=.004 I think. Not sure why they did that, but given that Arp says there are many associations with very close galaxies, it may be cutting out some of the most interesting part of the data for testing Arp.