For the longest time, if “separate verification” existed in a scientific study, then the theory was confirmed. If “separate verification” was found in tales of the paranormal, the obviously it was either mass hallucination, cryptoamnesia, or a variety of flukes.
But really: if we do perceive things like ghosts, UFOs or such, has more to do with our human minds than with any “fact” of their existence. Because myths and magic are human.