Two deads are better than one

Gary Schwartz has taken scientific protocol to new heights. We've all heard of double blind studies. To further improve the reliability of science he's now given us "double deceased" experiments.

Each [experiment] takes place in two different centres, there are two mediums and two sitters who have never met each other and each deceased person the medium alleges to contact has to bring another deceased person with them for verification. The readings are then scored for accuracy.

Medium: What is your name?

My dead grandma: Elizabeth.

Medium: Is that true?

My dead grandpa: Affirmative.