Klein’s dissertation Essays in Competition Economics (2020) consists of 4 essays on competition economics and policy. One of the essays deals with the novel issue of algorithm collusion: 'One such concern is that intelligent, self-learning pricing algorithms may work out how to ensure high prices...This would be akin to collusion, but without any overt act of communication required'. The other essays explore financial benchmark rate collusion, review the analysis of merger events, and offer an analysis of cartel stability. The full text of the dissertation can be viewed online.

The conferral of his doctorate and his PhD defense took place in a ‘hybrid’ PhD ceremony (live event with online participation due to COVID-19 measures) held at the UvA's Lutherse kerk main auditorium.