I had five flights last week. I was in the first group each time (in F on four, the fifth was a lightly loaded commuter flight with one boarding call) but, based on posts in this and other threads, made sure not to be first in line. Not one of the people who was first in line was called aside for a secondary screening, though one or two of the people in front of me were.

Maybe they saw that passengers have figured out that the first person in line is (was?) generally chosen, so they've switched to another strategy.