Poltergeist are a collective of semi form ghosts conglomerated in a single location.
First and foremost is should be noted that there is no singular entity in a poltergeist, it is infact a psychokinetic mass of semi formed beings that if more powerful might have formed into ghosts focused into one area. though the term "A poltergeist" is technically correct, to deal with it as though it was a singular intelligence would be a mistake.
Poltergeist are an unintelligent form of incorporeal undead. That isn't to say they aren't capable of cleverness, but they operate on pure emotions rather then any kind of rational plan. They lash out simply because they hate. there is nothing deeper there. as well, as more semi-formed ghosts are made part of it, the more powerful it becomes, even reportedly being able to over power entirely formed semi intelligent incorporeal undead.
In such an event the poltergeist can become a devastating event to deal with, formidable as it is normally. comprised of multiple memories, goals can become confusing, and tactics varied. It is note worthy that despite extreme cases poltergeist are bound to a single area, though maximum size isn't set until it's creation, one recorded covered over 3 square kilometres and was able to terrorize its entire length for long periods of time.
Poltergeist however, are not naturally forming and are generally tied to an event or reason for being there. mass suicides, disrupted rest, and mass murder are among the chief reasons they form, but there are possible others. Learning their reason for existing is the primary way to deal with it. usually by exacting revenge, stopping the cause for mass suicide or settling the 'spirits' there are often the easiest way that does not involve vast amounts of magical resources to directly combat the force of the poltergeist.
Direct confrontation is never advisable, and often entering the area it exists is dangerous until the time in which you are going to set them to rest.
Detection methods are similar to ghosts, however as they are necessarily malicious what starts of as simple shows of power, stacking chairs in odd ways, causing food left in an area to rot incredibly fast, ect, can quickly turn violent and if you suspect an area to be inhabited by a poltergeist vacate immediately and research this location.
Under no circumstances should you ever return unprepared. items left behind are forfeit, and sending other persons to retrieve them will resault in loss of life.