I'm an APD candidate with a PhD in Social Anthropology from the University of Edinburgh. I just spoke with a family friend who was in the DC office who came in as an experienced hire as an Associate. When I asked him about the PST, he said that APD candidates don't usually have to take it. He also had a role in developing tools and resources for PhD to Consulting new hires, so I imagine he'd have some insight on this.
I've seen this depends on region, but can anyone tell me if this is the case for the London office as well (which I'll be listing as my first choice)?