Summarizing 400 studies over the past 60 years, the report concludes that humans perform only “the same as or slightly better than chance.” Given that the TSA has spent almost a billion dollars on the program, that’s a pretty poor record.

http://www.theverge.com/2013/11/13/5100702/tsa-screening-works-only-a-little-better-than-chance-according-to

This includes extensive studies of the TSA SPOT programme over 2011 & 2012