'Say it again, Sam' - and create a winner

Star Wars is revealed as one of the most influential movies by the number of times it is referenced in other films.

As writers, actors and directors jostle for favour following the Oscar and Bafta award nominations, scientists have discovered the true measure of a film's worth is not how many gongs it wins, but how many times later film-makers reference it.

An analysis of nearly 15,500 films found it was possible to predict which ones would be considered among the greatest by looking at how often their themes, images or overall message were picked up by other directors many years later.

The researchers said their method of working out the cultural, artistic or historical significance of films could even be applied to other spheres of artistic and scientific creativity, from literature to physics.

"Directors keep coming back to movies that are significant," said one of the study leaders, Professor Luis Amaral, of Northwestern University in Evanston, Illinois.

"If you show a little bit of Psycho, such as referencing the shower scene, you are putting that whole movie in front of the viewer of the new movie."

The study included only references made 25 years after a film's release to ensure long-term influences.

The films with the most long-lived influences were The Wizard of Oz, Star Wars, Psycho, Casablanca and Gone with the Wind.

The study, published in the Proceedings of the National Academy of Sciences, analysed the 15,425 US-produced films listed in the Internet Movie Database to see whether there were any ways to predict whether a film would get on to the US National Film Registry of the Library of Congress.

It analysed 42,794 citations in the film database that connect one film to another, such as the dialogue about not wanting to be with a man who runs a bar in Casablanca in the 1989 film When Harry Met Sally, referencing the 1942 film Casablanca, starring Humphrey Bogart and Ingrid Bergman.

The scientists found big box office returns, Oscar wins and good reviews were not a reliable guide to long-term success.

"Ultimately it is the creators, the film-makers themselves, who will determine which movies are important," Amaral said.