Question: what horror films are based on true stories?
Answer: The Exorcist (1973) ... 
The Texas Chainsaw Massacre (1974) ... 
A Nightmare On Elm Street (2010) ... 
Child's Play (1988) ... 
The Amityville Horror (2005) ... 
Psycho (1960) ... 
The Girl Next Door (2007) ... 
The Conjuring (2013)