Number-crunchers have worked out the mathematical formula behind the perfect horror film.
Their complex equation has identified why thrillers like Psycho and The Blair Witch Project make such great spine-chillers.
The mathematical model, which looks like this, (es+u+cs+t) squared +s+ (tl+f)/2 + (a+dr+fs)/n + sin x - 1, shows what elements of suspense, realism and gore combine to make a blood-curdling scary movie.
Based on their formula, researchers found that The Shining, the 1980 Jack Nicholson film based on the Stephen King book, made the perfect horror film.
The researchers spent two weeks watching a selection of films in the horror canon, including The Exorcist, The Texas Chainsaw Massacre, and Silence of the Lambs.
They discovered that suspense comprised four essential categories: escalating music (es) the unknown (u), chase scenes (cs) and the sense of being trapped (t).
Because suspense is one of the most important qualities in a frightening flick, the equation is (es+u+cs+t) squared before shock (s) is added to the formula.
The Shining, where the suspense is built up gradually with frightened boy Danny's premonitions and flashbacks, is the perfect example.
The experts say that for a movie to be truly terrifying it must be realistic.
That's why the next part of the equation sees true life (tl) and fantasy (f) added together and divided by two (tl+f)/2 to find a medium between a plot which is too unrealistic and too close to life.
The smaller the number of characters in a horror movie, the more the audience can empathise with them.
And the darker the scene, the more frightening the characters' isolation can become.
So the formula looks at whether the characters are alone (a), in a dark environment (dr) and the film setting (fs) and divides it by the number of people (n) in the film (a+dr+fs)/n.
Researchers say the The Shining's isolated setting, with the family living in a huge hotel closed down for the winter, and the shower scene in Hitchcock's Psycho, where Janet Leigh is alone, naked and at her most vulnerable, is a shining example of this part of the formula.
If a character or situation falls into stereotype this detracts from the suspense and fear.
So the experts have taken blood and guts (Sin x) and subtracted it by the stereotypes (1), to make Sin x - 1, saying Jack Nicholson's character in The Shining turned into the total opposite of a protective father figure.
The research was carried out for Sky Movies, which will be showing The Shining and other scary movies this weekend.
