Originally Posted by Orion

I believe there is a random sample and it is likely very small. Anything else is targeted. It must be easier for an agent to call it "random" than to say, "this is a targeted search and I can't tell you what the trigger was".
The random sample is valuable because it tells the agency what the typical traveler looks like. The inspectors don't like the random sample because it doesn't tell them what to look for.