One-mode and two-mode networks, for social groups in Natchez Mississippi and terrorist roles in the Noordin Top terrorist network. How many groups can be identified, and how? Recommender systems are large-scale extensions of these simple networks, with computational difficulties. They were used in the Trump election campaign of 2016, to saturate Facebook and Twitter with false attacks on Mrs Clinton.

Brief biography:
Murray Aitkin is an Honorary Professorial Fellow (Associate) in the School of Mathematics and Statistics, University of Melbourne, and a 2021 Shayle Searle Visitor to the Statistics Group at VUW. He has held chairs of statistics at Lancaster University, where he was foundation Director of the Centre for Applied Statistics, and at Newcastle University (UK) plus at Tel Aviv University. For many years Prof Aitkin was a senior statistics consultant to the US National Center for Education Statistics.