There are some definitions that need to be brought to people attention in the discussion of paranormal phenomena at that is the difference between a classical haunting and that of poltergeist intrusion.
Classical Haunting:
This phenomena is a associated with a vary traumatic event such as a murder or other sudden death phenomena where the person in question died before their time and they had no time to do all the things they wanted in their lives; this causes their life's force (Soul if you will) great pain and they wish to complete what ever business it was they had before they are ready to move on.
There have been instances in the paranormal literature where the haunting has proved to be genuine where things have gotten so bad that people living in the place where the Haunting is, that they been forced to move away. In these cases the pain of the ghost is so bad, that it has turned in on its self and become malevolent and dangerous that it takes its pain out on the living, in some case actuality causing physical harm.
Classical Hauntings are usually long term phenomena lasting years, or even centuries and are not easily resolved. There have been instances over the centuries of having a location where there is a haunting blessed by a Catholic Priest or in extreme cases having the right of exorcism performed (Normally carried out on an individual where it is confirmed that demonic possession has taken place, and the Priest may only carry out the right if given permission to do so by his Bishop, as exorcism is extremely dangerous and has been known, on occasion to kill) and making the situation far worse.
Poltergeist:
Poltergeist phenomena (Genuine ones) compeered to that of the classical haunting are normally short lived phenomena though there are well documented cases which have lasted a century or more: they are normally persons who died but got lost on the way to the next plain of existence, and are stuck between this world and the next.
Poltergeist activity can range in severity form the mildly annoying (Moving a vase to a different location) right up to extremes of violence, weather these be aimed at a single person to a family with recorded cases of deaths.
Some Poltergeist phenomena are the result of a person who lead a full life but whom wants more, and so greedy for more life do they become that they cannot except the fact that they've died and so the wonder around causing mischief.
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The above is a greatly simplified version of both phenomena I hope it helps. I have seen a Ghost many years ago and her story goes like this.
In the UK during the First World War there where many Military Hospitals built to deal with the many wounded service personal brought back form the front; at this Hospital in question a nurse develops a deep relationship with one of the wounded officers there. At first it seemed that this officer was going to pull through, but unexpected complications set in and he died, in the grounds of the hospital there is a chapel (This is still there) the nurse in question was so deeply affected by the death of this officer she'd formed a relationship with that she jumped to her death form the bell tower of the chapel.
I only saw her briefly but when I did she was walking towards part of the ground under the chapel bell tower (Where she lay when she died most likely and then vanished).
Regard to you.
Cyber-Angel