> There are no randomized controlled trials that parachutes save lives.

It's a good thing "randomized controlled trials" aren't the only kind of empirical evidence, then.

We know the limits of how fast a human can safely land. Parachute manufactures have to prove that their designs meet the minimum performance specifications to achieve a safe speed. This proof is not invalidated by the fact that it doesn't include throwing some poor bastard with a placebo parachute out of an airplane to demonstrate that he dies on impact.

Also, the answer to your original question is yes. There are numerous studies showing that multiple monitors improve productivity.