However it is being used right across the board for a vast number of experiments in testing things like ESP and prayer and other situations where the direct relationship between the subjects is an important factor.
Watch the following clip of a documentary.
So, how do we know it's not just psychological if it only works on a believer? More bluntly, what use is it if it doesn't work on a nonbeliever? Can you imagine a chi master begging his fight opponent to believe before the fight begins?