On the Implementation of Random Bag Checks in a Busy Transit System

If people are walking past in a constant stream of groups of twenty, it is not possible to randomly select an “individual” for screening.

The best you can do is to randomly select a “moment”, at which time you will non-randomly select an individual from the group of twenty in front of you.

Same holds true for streaming crowds of ten or thirty.. once you are below ten, you might be able to randomly select in some meaningful way, and above thirty I think you’d be lucky if you could catch someone’s attention long enough to get them to stop for a screening at all.