OK, well it can't really be correlated to one-way vs round trip because at that point you've put your BP away, and between people with CLEAR getting to jump the line, the fact that sometimes a slower pax tells people to go around them, and some setups have two lines feeding into a single detector, I don't see how they could reliably connect the two.

Maybe they're doing demographic profiling, but as I said it feels more like it's just random every N passengers or maybe they have to do a certain number of randoms per hour and if you travel at off-peak times you're more likely to get selected or some other factor like that. Streaks happen. I had like 4 trips in a row of getting "randomly" selected but also I've now gone a really long time w/o one (of course now that I said that out loud... )