Sometimes we wish to believe what we really want to believe. Alone in a dark house, we feel vulnerable and thus we try to justify our unreasonable feeling of vulnerability by forcing an illusionary entity such as a GHOST.
However there are some stories which are quite strong to suggest that spirits do exist. How can civilizations as far apart as Indian, Native American, European and African or Japanese contain stories of ghosts and spirits even before any contact between each other? These are common things almost all cultures and traditions, so if one doesn't find evidence of the existance of spirits, one cannot say that this would be an evidence against the existance of spirits.
My grandmother (maternal, now deceased) used to tell me about a story just before the second world war. She was just 14, and her village was in Auschwitz, Poland. She heard of a curse to follow after a tomb of an Exorcist was demolished by the authorities. The villages protested but were pushed away. The tomb was a practice place for researchers who were peaceful naturalists. It was not something where black magic was practiced. Infact it was quite transparent.
The Exorcist took inside his grave some of his books on psychotherapy and other unexplained cases. His casket was said to contain many bottles of chemicals and other empty ones which he himself tabulated on a list to be burried with him.
Now this may or may not be related to whatever happened in Auschwitz. But the village elders said of a date when the curse might materialize, and it was the date of the first exterminations.
There are many things unexplained, some of whose answers might actually be scientific, involving energy waves and other influencing factors in our surroundings. They may be spirits as well...who knows.