Or have they? It depends a lot on who you ask. And whoever you ask the answer turns out to revolve around degrees of statistical probability. So the credibility or otherwise of all the research turns out to involve wading through book-length articles on statistical significance.
Although it isn't scientific, I think just listening to people's experiences and looking at the historical record across numerous cultures is enough to securely state that, at the very least, many people have and continue to experience the existence of disembodied intelligent consciousnesses, some of them apparently malicious and parasitic.
Of course that won't satisfy the hard skeptic who wants scientific evidence, but if what the Occult would generally suggest about demons is correct, then since they are more or less immaterial forces you cannot objectively capture and study them. Nevertheless, there's still the phenomenon of possession, as well as ghost sightings and other experiences with spirits or gods. The usual response is to simply classify all of it as either harmful neurosis or mere religious fantasies, which makes sense if you're a materialist, but again much of the world actually doesn't really believe strongly in materialism.
Even in Japan where secularism and science are mainstream, plenty of people believe in ghosts. In fact, after the great tsunami in Japan, there have been numerous ghost encounters reported in the affected regions.
http://www.usatoday.com/story/news/worl ... /79871530/
My experience in Japan also suggests that most people there have a passive belief in spirits and ghosts, though they maybe haven't articulated a strong opinion on the matter.
And it's also a very nasty debate.
I wonder if it doesn't stem from the fact that materialism is fundamentalist about its ontology. It cannot concede an inch to alternative worldviews because its stated premises and the world it describes completely depends on deducing all phenomena to physical forces with no room for what it would term the 'supernatural' (that word is problematic because if ghosts exist they're not beyond nature). It is curious how offensive and antagonistic some self-identifying skeptics can get when you discuss the possibility of spirits actually existing in some way beyond our ordinary material reality.
They're clearly emotionally invested in their worldview. Maybe it is an unspoken fear that as they stare into the abyss, they would be horrified to know the abyss is staring back at them, and that on the far side of death it isn't necessarily the blank unconscious eternity they might be looking forward to.
So, my take is, interesting, kind of, possible, perhaps, but unless one is unfortunate enough to require the services of an exorcist, probably a subject better left alone.
Interestingly, it isn't seen like this in a place like Nepal. I know an exorcist in Kathmandu and he's quite casual about it. He lives in an ordinary apartment with his family. I get the impression the community see him as a good Lama with a certain expertise that is needed once in awhile.
I think the Western fears about exorcism and demons are heavily influenced by Catholicism which is basically the "go to place" and representative institution in the Western world when it comes to discussing the subject. Hollywood also contributes a lot to the common understanding. In Christianity, if you're dealing with demons you're effectively speaking to the Devil himself or his direct agent, which is probably pretty terrifying if you're a devout Christian. In a Buddhist context, however, there's various classes of beings (devas, asuras, pretas and so on) you might be dealing with, most of which are of limited power. I recall that Tibetan medicine specifically addresses their respective symptoms.