The majority of what people think ghosts are is actually based on superstition and folklore. There has been some serious scientific work done and what was discovered is the topic of this video.
The studies are;
1894 The SPR’s Census of Hallucinations
1948 D.J West’s Mass Observation Survey
1974 McCreeley & Green
1990’s D.J. West’s Pilot Survey
2002 Dr Hilary Evans Seeing Ghosts
2008 Wiseman and Watt Online study
2008 Dave Wood (ASSAP Chair)
2009 Romer & Smith: The Accidental Census
2010 -2012 Strange Survey, Rebecca Smith’s Ph.D. study