SOME PARANORMAL GROUPS!

I would like to know how it is that a group of paranormal investigators can go into a building investigate it for a few hours and come out and say it's not haunted. After all the investigations we have done we have not been able to do this and a good investigator knows that paranormal activity does not occur all the time. It takes time and more then a few hours of investigating to say this even then we cannot say for sure that a building or location is not haunted just because we did not witness any paranormal activity. We must investigate and research and after all is said and done all we can say is we did not witness any paranormal activity during the investigation. But for the investigators that can do this you have all have been watching to much TV.