In the 1970s in Canada, a group of parapsychologists created an unusual experiment (video here of show about it). They believed they could make up a fictitious ghost with a story about a life that never existed and concentrate on it enough to produce ghostly results created by expectations and the minds of the people participating, all of whom were not known to be psychic. Here was the story they devised:
Philip was an aristocratic Englishman, living in the middle 1600s at the time of Oliver Cromwell. He had been a supporter of the King, and was a Catholic. He was married to a beautiful but cold and frigid wife, Dorothea, the daughter of a neighboring nobleman. One day when out riding on the boundaries of his estates Philip came across a gypsy encampment and saw there a beautiful dark-eyed girl raven-haired gypsy girl, Margo, and fell instantly in love with her. He brought her back secretly to live in the gatehouse, near the stables of Diddington Manor - his family home.
For some time he kept his love-nest secret, but eventually Dorothea, realizing he was keeping someone else there, found Margo, and accused her of witchcraft and stealing her husband. Philip was too scared of losing his reputation and his possessions to protest at the trial of Margo, and she was convicted of witchcraft and burned at the stake. Philip was subsequently stricken with remorse that he had not tried to defend Margo and used to pace the battlements of Diddington in despair. Finally, one morning his body was found at the bottom of the battlements, whence he had cast himself in a fit of agony and remorse.
The group eventually was able to produce table rocking, rapping, and more activity, but no actual apparition. It was considered a success and subsequent experiments were done using other fictitious people.
So, what was happening? Was it PK (psychokinesis--movements created by thought)? A latent psychic ability giving rise as the group worked together to one goal? Was it possibly the attracted another spirit by concentrating? We can't make any conclusions. Had the evidence been, say, an EVP of someone saying "I am Philip," we can't make any assumptions and, as I know from the ghost hunting field, even if it said "I am Philip" that could be projected from a person in the group or even something else using that name.
This is a tough field of study, but we are learning much from experiments such as this. I plan in 2012 to do a lot of unusual experiments in the field and we can work together on here, going over the findings and making some conclusions.