The Conjuring's two winning formulas for topping the box office is due to Warner Bros. promoting the film as 'based on a true story' and through word of mouth from audiences who were the first ones to watch it during its earlier release.

"It clearly had the elements that would result in good reviews, so we were very aggressive with early screenings, and that got the word-of-mouth going," Dan Fellman, president of Warner Bros. distribution, said.

"It was a horror film, but nobody dies and the execution and acting is such that it played much more like a classy thriller than an exploitation film."

The James Wan horror feature had a budget of $19.5 million and New Line/Warner Bros. had to gamble releasing a horror film in summer where big-budget superhero movies often dominate the theatres.

Surprisingly, The Conjuring managed to lead the box office race during its opening weekend, raked in a stunning $41 million and debuted at no. 1 from July 19 to 21.

Moreover, the character played by Vera Farmiga, paranormal investigator Lorraine Warren; the Perron sisters and the Conjuring house in Rhode Island also caught the audience's interest, which drove The Conjuring's popularity, passed on to those who still have not watched the film.

Even film critics praised the film, which is a rare thing for horror movies.

The real life Lorraine Warren and her husband, Ed, were involved in the investigation on the demonic possessions that happened to the Perron family at a farmhouse in Burisville in the 1970.

Lorraine, now 86, thinks that the team behind The Conjuring "did a pretty good job." Andrea Perron, one of the five sisters who encountered the horrors at the farmhouse, admitted that "some elements of the film are very accurate and some are fiction" and noted that she and Lorraine had handed over their files and writings to the film production.

Andrea told The Providence Journal: “The cast is perfect," and that “The children resemble us as children and have our personalities as children."

She has become a writer and has self-published two volumes of trilogy about hauntings titled House of Darkness, House of Light.

View the slideshow to see some of the films that are based on a true story.