And I stand by my point that a supernatural being cannot be proved by science, because by its nature it is supernatural, and therefore does not follow scientific laws. This renders the being's existence impossible to prove scientifically. I'm still baffled that some people don't understand this simple concept...
Mediumship is a phenomenon that can be tested. A supernatural or discarnate entity can be shown to be the simplest explanation of certain evidence, like in the paper "The Problem of Seth's Origin" or the case of the dead chessmaster who communicated details of his life and played a game characteristic of the prior personality. The hypothesis that is used to explain the existence of this type of personality is called 'survival'.
http://www.aeces.info/Top40/top40-main.shtml