This is getting tedious. I've posted several links on that, granted there are several threads and they may have been in other threads.
And you can read extensively about simulated runs through these security and of simulated aircraft attacks. Granted, and for good reason, often the results are classified.
Why don't you just google it and come back with your conclusion?
Nothing in this thread. I just double-checked. I've seen posts on how the TSA is a lot less effective than a private firm (which is presumably far more expensive), but from what I read that was before scanners were implemented.
My quick google search didn't reveal any such studies.